Electric field quenching of graphene oxide photoluminescence

Type: Graduate
Author(s): Alina Valimukhametova Physics & Astronomy Fabian Grote Physics & Astronomy Bong Han Lee Physics & Astronomy Thomas Paz Physics & Astronomy Conor Ryan Physics & Astronomy
Advisor(s): Anton Naumov Physics & Astronomy
Location: Zoom Room 3, 02:15 PM

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in nanodevices such as bio and gas sensors, solid-state supercapacitors and solar cells. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to allow fine-tuning of its optical properties in the device geometry, new physical techniques are required that, unlike existing chemical approaches, yield substantial alteration of GO structure. Such a desired new technique is one that is electronically controlled and leads to reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modeling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/polyvinylpyrrolidone films with up to 6% reversible decrease under 1.6 V µm−1 electric fields. On an individual flake level, a more substantial over 50% quenching is achieved for select GO flakes in a polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modeled on a single exciton level by utilizing Wentzel, Kremer, and Brillouin approximation for electron escape from the exciton potential well. In an aqueous suspension at low fields, GO flakes exhibit electrophoretic migration, indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.

Cloudy with a Chance of Stars

Type: Graduate
Author(s): Joe Vazquez Physics & Astronomy Jaq Hernandez Physics & Astronomy Matthew Nuss Physics & Astronomy
Advisor(s): Kat Barger Physics & Astronomy
Location: Zoom Room 1, 02:39 PM

The Smith Cloud is a fast-travelling gas cloud that is currently hurtling towards the Milky Way galaxy at about 170,000 miles per hour. If the cloud is able to reach the Galactic plane, it has the potential to supply the Milky Way with at least 2 million suns worth of gas. This gas can be used to make new stars, planets, and even meatballs. In this project, we use observations taken with the Hubble Space Telescope and the Green Bank Telescope. We fit our spectroscopic observations with line profiles to quantify the amount of gas and its motions. We then take measurements of the low- and high-ionization species of two small cloud fragments that lie adjacent to the main body of this large gas cloud. This enables us to constrain the processes that impact the Smith Cloud as it traverses the Galactic halo. Our investigation could provide great insight on how galaxies capture the gas that they use to form stars and planets.

Experience with Extrinsic Rewards does not Undermine Intrinsic Motivation in Rats

Type: Graduate
Author(s): Sara Bond Psychology Kenneth Leising Psychology Marisa Melo Psychology Tanner Raab Psychology
Advisor(s): Kenneth Leising Psychology
Location: Zoom Room 4, 02:15 PM

Intrinsic and extrinsic motivation satisfy biological needs or desires. Behavior that is intrinsically motivated is not followed by any apparent reward, except for the behavior itself. Behavior that is extrinsically motivated is followed a separate, observable reward. The overjustification hypothesis states that after engaging in behavior as a means to an extrinsic reward, there will be a reduction in one’s intrinsic motivation to engage the behavior. The current study observed whether the overjusitification effect occurs in rats when using lever pressing as a measure of intrinsic motivation. For all rats, intrinsic motivation was measured in Phase 1 by the number of lever presses made by each rat in the absence of any observable reward. In Phase 2, one group continued to lever press without reward (Control), while the other group received a sucrose pellet (extrinsic reward) for each lever press. Lever pressing in the absence of reward (intrinsically motivated) was again measured in Phase 3. The extrinsic reward group emitted more lever pressing in the sessions at the start of Phase 3. Lever pressing decreased thereafter, but stabilized at a higher rate than the control group. The groups were then switched before Phase 2 was repeated. The overjustification effect was not observed in our study, but rather, reinforcement protected the response from habituation.

You Are What You (Are Willing To) Eat: Willingness to Try New Foods Impacts Perceptions of Sexual Unrestrictedness and Desirability

Type: Graduate
Author(s): Matthew Espinosa Psychology Hannah Bradshaw Psychology Alexander Darrell Psychology Sarah Hill Psychology Summer Mengelkoch Psychology
Advisor(s): Sarah Hill Psychology
Location: Zoom Room 6, 01:02 PM

Here, we examine the impact of one’s willingness to try new foods on others’ perceptions of sexual unrestrictedness and desirability as a sexual and romantic partner. Guided by insights from past research, we hypothesized that targets who are willing to try new foods would be perceived as being more desirable sexual and romantic partners (Study 1) and as being less sexually restricted (Studies 2-4) than targets who are unwilling to try new foods. Results supported this hypothesis (Studies 1-4) and indicated that this pattern is specific to willingness to try new foods, and not willingness to try new things, generally (Study 3). Additionally, results revealed that the relationship between willingness to try new food and perceptions of sexual unrestrictedness are driven by perceptions of target’s relatively lower levels of sexual disgust sensitivity and not by the belief that the target is in better health or has superior immune function (Study 4). Together, these results suggest that people’s willingness to try new foods may impact how they are perceived by prospective dates and mates.

Lecture Fluency Impacts Instructors' Ratings of Other Instructors' Teaching

Type: Graduate
Author(s): Paige Northern Psychology Addison Babineau Psychology
Advisor(s): Uma Tauber Psychology
Location: Zoom Room 3, 03:35 PM

There are many factors that can impact students’ evaluations of instructors’ teaching. Lecture fluency (i.e., the ease with which a lecture is delivered) is one factor that can impact students’ evaluations. Recently, researchers have examined how fluent lectures (very polished lectures during which the instructor makes appropriate eye contact and exudes confidence) compared to disfluent lectures (lectures during which the instructor does not make eye contact and does not display signs of confidence) impact students’ evaluations of instructors. Students who watch fluent lectures typically evaluate the instructor more favorably relative to those who watch disfluent lectures, even when the content in both lectures is identical (Carpenter, Mickes, Rahman, & Fernandez, 2016; Carpenter, Northern, Tauber, & Toftness, 2020; Carpenter, Wilford, Kornell, & Mullaney, 2013; Northern, Tauber, St. Hilaire, & Carpenter, in prep; Toftness, Carpenter, Geller, Lauber, Johnson, & Armstrong, 2017). All of the research on lecture fluency has focused on students’ evaluations of instructors, but the delivery of a lecture may also impact instructors’ evaluations of other instructors’ teaching. On the other hand, instructors have much experience both watching and delivering lectures, and it is possible that they may rely more on their experience when evaluating instructors rather than the fluency of a lecture. In this study, students and instructors watched a video of a lecture. The lecture was delivered either fluently or disfluently, and the content was the same in both lectures. After watching the lecture video, students and instructors rated the instructor on several evaluation items. Novel to the current study, instructors who watched a fluent lecture gave significantly higher instructor ratings compared to those who watched the disfluent lecture. Replicating prior work, students who watched a fluent lecture gave significantly higher instructor ratings relative to students who watched the disfluent lecture. Thus, the delivery of a lecture rather than the content of a lecture can have a strong impact on instructors’ evaluations of other instructors’ teaching.

Effects of Pollen Limitation on Seed Production in the Pale Pitcher Plant

Type: Graduate
Author(s): Karis Kang Biology John Horner Biology
Advisor(s): John Horner Biology

Pollen transfer among flowers contributes to genetic diversity and the maintenance of plant populations through the production of seeds. Decreased pollen receipt can result in fewer offspring. This is known as pollen limitation. We conducted field and laboratory experiments in a population of Sarracenia alata in Leon County, Texas in 2019 to examine 1) the effect of floral herbivory by the pitcher plant moth, Exyra semicrocea, on pollen availability and 2) the impact of pollen receipt on seed quantity and 3) seed quality. We found that floral herbivory significantly decreased the number and mass of anthers in flowers, and that a high pollen load significantly increased the number of seeds produced compared to low-pollen and control flowers. We found no differences in offspring quality among different pollen treatments based on germination traits. Pollen limitation occurs in S. alata and may pose a conservation risk when paired with other ecological disturbances.

Predator-Prey Dynamics in an Urban Forest: Assessment Using Raptor Predation on Prey Mimics

Type: Graduate
Author(s): Amber Schenk Biology Amanda Hale Biology Tom Stevens Biology
Advisor(s): Amanda Hale Biology

Predator-prey dynamics play an integral role in shaping and regulating wildlife communities; however, recent studies have shown a decoupling of these relationships in urbanized areas. Trickle-down effects from the disruption of this trophic interaction have the potential to produce impacts that are far-reaching, altering other critical dynamics within the ecosystem. The purpose of my study was to characterize raptor activity and levels of predation in a large urban forest, the Great Trinity Forest in Dallas, TX. To quantify the extent of urbanization, I used ArcGIS Pro’s (version 2.2.0) image classification wizard with supervised, object-based classification on 50-cm pixel resolution, multi-band remote sensing imagery to estimate the percent of impervious surface. Then, from May to August 2019, I conducted weekly raptor surveys and deployed urethane foam prey mimics (snakes and mice) at 18 survey locations along an urban-to-rural gradient within this forest. In total, I detected 161 raptors representing 8 species throughout the season and found no relationship between raptor activity or diversity and degree of urbanization. Of the 732 prey models deployed, 61 showed signs of being depredated whereas 23 were missing and therefore had an unknown fate. Similar to the raptor results, overall predation on mice and snake models showed no relationship with degree of urbanization. Based on markings on the depredated models and photographs from field cameras, raptors appeared to target the snake mimics with no evidence of predation attempts on mice. And finally, I found no significant relationship between raptor activity and predation on snake models. Collectively, these results suggest either increasing levels of urbanization have no effect on raptor-prey dynamics within the Great Trinity Forest or there is low predatory response from raptors in regard to prey mimics.

Ectoparasite loads of Texas horned lizards (Phrynosoma cornutum) living in small towns

Type: Graduate
Author(s): Mary Tucker Biology Stephen Mirkin Biology
Advisor(s): Dean Williams Biology

Ectoparasites are a vital but often overlooked part of ecosystem dynamics, which have been shown to be negatively correlated with growth and decreased body condition in various vertebrate species. Texas horned lizards living in natural environments are known to harbor red mites (Acarina sp.), but the impact and density of these mites on lizards living in urban environments is not well known. Using weekly surveys during the summer of 2018, we examined the ectoparasite loads on Texas horned lizards (n = 87) from 11 different sites in Kenedy and Karnes City, Texas. We counted mites and recorded where they were found on the lizard’s body. We also determined the sex, age (juvenile versus adult), and body condition (body weight/SVL) of each captured lizard. We found significant differences in the number of mites between males and females, with males exhibiting heavier parasite loads, and also between different sites within the same town. We found no correlation between body condition and number of mites present. We present the first known research of ectoparasite loads of Texas horned lizards from an urban environment. Although the sample size is small, our data suggest that ectoparasite loads of Texas horned lizards from natural environments have lower mite loads than lizards found in an urban environment. These findings deserve further exploration to see if urban environments play a role in increased parasitism.

POROUS SILICON NANOTUBES AS POTENTIAL VECTORS FOR SMALL INTERFERING RNA DELIVERY

Type: Graduate
Author(s): Nguyen Le Chemistry & Biochemistry
Advisor(s): Jeffery Coffer Chemistry & Biochemistry Giridhar Akkaraju Biology

In cancer therapy, nucleic acid-based therapeutic strategies have been extensively investigated to suppress mutated gene expression, thereby inhibiting cancer cell growth. Among the approaches, small interfering (siRNA)-mediated gene silencing has been envisaged as a promising therapeutic approach to silence specific gene expression by targeting mRNA of the unwanted gene for degradation, thereby readily controlling cellular functions. However, delivery of small interfering RNA (siRNA) has been known to encounter multiple challenging barriers, such as blood circulation and cellular internalization, thus limiting the potential merits of this therapeutic strategy. While non-viral vectors have been preferred owing in part to better immune system compatibilities, porous silicon (pSi) with various geometric shapes (e.g. platelet and discoid) have recently been demonstrated as exceptional delivery carriers of siRNA in various disease models. Here our initial in vitro studies show that silicon in a unique one-dimensional porous nanotube structure (pSiNTs) can serve as a promising vector for delivery of siRNA to limit target gene expression, thereby expanding the library of possible nanostructures of Si in delivery of siRNA.
In this work, we demonstrate that pSiNTs after being functionalized with 3-(aminopropyl)triethoxysilane (APTES) can deliver enhanced green fluorescence protein (EGFP)-targeting-siRNA via electrostatic conjugation and suppress EGFP expression in HeLa cervical cancer cells by up to 50%. Cytocompatibility and biodegradation of the functionalized pSiNT matrix upon siRNA delivery are characterized by ATP quantification assays (CellTiter Glo) and Transmission Electron Microscopy imaging (TEM) respectively. These results encourage further development of pSiNTs in therapeutic applications.

Improving habitats for bats: What makes a bat-friendly residential swimming pool?

Type: Graduate
Author(s): Elizabeth Agpalo Environmental Sciences
Advisor(s): Victoria Bennett Environmental Sciences

For urban environments to support bat communities, resources need to be readily available, such as water. For example, bats typically use urban water sources, such as drainage ditches, lakes, and ponds. However, in areas where temperatures are consistently high and rainfall limited, these sources tend to be ephemeral. During these periods, bats utilized residential swimming pools. If pools were more attractive to bats, we may be able to improve urban habitats for bats both in terms of abundance and species diversity. We, therefore, set out to determine whether size, shape (round of square), lighting, and treatment type (chlorine, salt, or mineral) encouraged bats to drink at pools. Thus, we conducted behavioral surveys at 14 pools using thermal cameras and acoustic detectors to record bat foraging and drinking activity. Our results demonstrated that while shape did not influence pool use, treatment type, lighting, and size did. With this information, we can better advise interested residents in urban neighborhoods how better to make their backyards more bat-friendly.

Illinois agriculture: An examination of the relationship between annual corn crop yield and the application of Atrazine.

Type: Graduate
Author(s): Dalton Allen Biology
Advisor(s): Esayas Gebremichael Geological Sciences

Herbicides are chemicals frequently used in agriculture to manage or remove unwanted vegetation (i.e., weeds) that may negatively impact crops through resource competition. Through the elimination of these competitors, losses in crop yield may be reduced thus increasing cropland productivity. Atrazine is an herbicide that is widely used in the United States for the control of weeds that is predominately applied in the agriculture of corn, sorghum, and sugarcane. This is of interest to Illinois agriculture, as according to the United States Department of Agriculture (USDA), Illinois is a major agricultural producer of corn and soybeans with corn accounting for 11 million of Illinois’ 27 million acres of cropland. Further, Illinois possesses an agricultural industry that produces more than $19 billion annually of which corn accounts for more than 50 percent. It is due to the economic importance of corn crops to the state of Illinois and the widespread use of Atrazine in the agriculture of corn, that this project seeks to examine the relationship between Illinois annual corn crop yields and Atrazine application. This relationship will be assessed through analysis of spatial data acquired from the USDA for Illinois Atrazine application and corn crop yield.

U-PB DETRITAL ZIRCONS OF SYNOROGENIC CARBONIFEROUS DEEP-WATER CLASTIC DEPOSITS IN THE OUACHITA MOUNTAINS, ARKANSAS, UNITED STATES

Type: Graduate
Author(s): Shaun Prines Geological Sciences Walter Manger Geological Sciences Xiangyang Xie Geological Sciences
Advisor(s): Xiangyang Xie Geological Sciences

The southern margin of the North American continent transformed from a passive margin to an
active margin during the Ouachita orogeny. Thick and near–continuous Paleozoic successions in
the Ouachita Mountains provide a unique opportunity to document changes in both
sedimentation and tectonics. In contrast to well-documented Taconic, Acadian, and Alleghenian
orogenic events, limited detrital zircon studies of the Ouachita orogeny and associated
successions have been published, and sediment sources of these deep-water, synorogenic clastics
remain less constrained.
In this study, a total of six outcrop samples (n=617) from the Mississippian Stanley Group and
Lower-Middle Pennsylvanian Jackfork and Johns Valley Groups were collected and processed
for U-Pb detrital zircon geochronologic analyses to depict sediment sources and dispersal
patterns during the Ouachita orogeny. Results show that the age distributions of the
Carboniferous deep-water clastic deposits in the Ouachita Mountains are characterized by major
peaks of the Paleozoic (~350-500 Ma), Grenville (~900-1350 Ma), and Midcontinental GraniteRhyolite (~1350-1500 Ma), minor peaks of Yavapai-Mazatzal (~1600-1800 Ma) and Superior (>
~2500 Ma) provinces. These deep water clastics share great similarities with the Appalachian
sources and are likely derived from similar sources. From the Mississippian Stanley Group to the
Pennsylvanian Jackfork and Johns Valley Groups, the Yavapai-Mazatzal population shows
marked enrichment (up to ~12%), suggesting Precambrian basement uplifts, possibly related to
the Ancestral Rockies to the northwest, might be another potential source. Compilation and
comparison show the Neoproterozoic age population (~550-800 Ma), most likely associated with
the peri-Gondwana terrane to the south, ranges from 3% to 35% within the Mississippian Stanley
Group. The variation indicates that the Stanley Group may have strong but short-lived local
contribution from the Gondwana terrane in addition to the regional Appalachian sources.
Overall, despite its proximal location, these Carboniferous deep-water clastic deposits in the
Ouachita Mountains received limited contribution from the Ouachita orogenic belt itself.

Trail Network Analysis of the TCU Tropical Biology Station

Type: Graduate
Author(s): Mary Tucker Geological Sciences
Advisor(s): Esayas Gebremichael Geological Sciences Dean Williams Biology

The new world tropics represent an area of unparalleled biodiversity. Unfortunately, it also represents an area of increasing habitat loss and consequently is in dire need of protection and conservation. The TCU San Ramon Tropical Biology Station located on the Caribbean slope of Costa Rica protects 100 hectares of primary and secondary forest and is a unique and ideal location for studying tropical biology. In the summer of 2018, we mapped an updated trail network at the station using a Bad elf sub-meter GNSS receiver in conjunction with Arc Collector. For this project we analyzed the distance each trail traveled through the 3 habitat types found at the station (primary forest, secondary forest, and pasture land), which will be used to aid the sampling efforts of my Master’s thesis project examining how mixed-species foraging flocks utilize the habitat protected by the station.

Quantifying the Hydrological Setting of Upper Flow Regime Channels of the Triassic Dockum Group of West Texas

Type: Graduate
Author(s): Samuel Walker Geological Sciences John Holbrook Geological Sciences
Advisor(s): John Holbrook Geological Sciences

The Triassic Dockum Group of the western Texas High Plains is studied in depth paleontologically, but until recently lacked a detailed sedimentological evaluation. Recent research of the Dockum Group in Palo Duro Canyon, Texas, provides new interpretations of the complex fluvial lacustrine strata of the comprising formations based on analysis of individual lithofacies. Identified within the lithofacies assemblages are numerous channel belts composed of upper flow regime bedforms. Observed upper flow regime bedforms in outcrop range from upper plane bed, antidunes, breaking antidunes, chutes and pools, and cyclic steps with increasing flow velocity respectively. These channel belts record extreme flow events from repeating massive storms that perpetuated throughout the Texas region of Triassic Pangea. These unique reservoir-quality channels are interpreted to be resultant of a megamonsoonal climate producing massive pulses of rapid flow allowing for the preservation of upper flow regime bedforms. While these channels are identified in outcrop they have not been quantified in distribution, variability in fill, connectivity and formative discharge.
This study aims to test the megamonsoonal hypothesis by quantifying the discharge of these channels and testing if the distribution density and paleodischarge of these channels is consistent with local dominance of megamonsoonal conditions. Upper flow regime structures are rarely preserved in the rock record and extremely difficult to observe directly during natural formation in modern rivers. Most of the equations used to quantify flow conditions for these structures are derived from flume tank experiments. These are applied to the upper flow regime bedforms found in outcrops of the Dockum Group to reconstruct paleohydrology. Current flume tank research reinforces Kennedy’s equations defining relationships between the wavelengths of stable antidune apexes (λ), mean flow depth (hm) and mean flow velocity (U). These equations are modified to account for different upper flow regime structures formed under increasing velocity and discharge identified in outcrop. Bedform distribution, size, and type are variables determined from outcrop measurement. Paleoflow velocities, Froude numbers and relative water depths are determined with an observed margin of error. Scaling relationships and field measurements provide constraints on channel cross sectional area and channel-belt density. This data along with grain size distribution provides tangible numbers for calculating formative discharge. Preliminary results align with data from flume tank experiments and are consistent with major floods produced by substantial storm events verifying the megamonsoonal hypothesis.

Campanian-Maastrichtian Ankylosaurs of West Texas

Type: Graduate
Author(s): Bryanna West Geological Sciences
Advisor(s): Arthur Busbey Geological Sciences

Deeper Exploration of the C*-Algebras Arising from Uniformly Recurrent Subgroups and their Relationship with Crossed Products

Type: Graduate
Author(s): Douglas Wagner Mathematics
Advisor(s): José Carrión Mathematics

A group is a mathematical construct that represents the symmetries of an object. These symmetries transform the object through what is called a group action. Graphs—Cayley graphs, in particular—provide a rich source of symmetries for forming groups. A graph and its group action can be modeled by a collection of infinite matrices known as a C*-algebra. In a paper in the Journal of Functional Analysis, Gábor Elek used dynamical systems called Uniformly Recurrent Subgroups (URS) to construct a new type of C*-algebra. We further develop understanding of these C*-algebras using tools from other areas of operator theory. In particular, comparisons with the well-known crossed-product construction have proven useful.

Graphene Quantum Dot Formulation for Cancer Imaging and Redox-Based Drug Delivery

Type: Graduate
Author(s): ELIZABETH CAMPBELL Physics & Astronomy Giridhar Akkaraju Biology Roberto Gonzalez-Rodriguez Chemistry & Biochemistry Kayla Green Chemistry & Biochemistry Tanvir Hasan Physics & Astronomy Bong Lee Physics & Astronomy Anton Naumov Physics & Astronomy Tate Truly Biology
Advisor(s): Anton Naumov Physics & Astronomy

Treatment of complex conditions, such as cancer, has been substantially advanced by a field of molecular therapeutics. However, many of these therapies are limited by the dose toxicity and lack the predictive power of tomography-guided approaches. Nanomaterial platforms can address these drawbacks, safely delivering therapeutics, concomitantly imaging their delivery pathways, and presenting sites for targeting agent attachment. Graphene quantum dots (GQDs) possess physical properties that are critical for biomedical applications, including small size (3-5 nm), high quantum yield, low cytotoxicity, and pH-dependent fluorescence emission. Nitrogen doped graphene quantum dots (N-GQDs) are now utilized as a platform for a targeted treatment formulation geared toward cancer therapeutic. Our work utilizes nitrogen-doped GQDs as an emissive platform for covalent attachment of a targeting agent (hyaluronic acid (HA) targeted to the CD44 receptors on several cancer cell types) and oxidative stress-based cancer therapeutic (ferrocene (Fc)). The synthesized multifunctional formulation is characterized and its efficacy evaluated in vitro. Elemental mapping indicates that the purified from reactants synthetic product has an average iron content of 0.64 atomic percent, suggesting the successful attachment of the therapeutic, while FFT analysis of TEM images confirms the crystalline structure of the GQDs. Although GQDs alone yield no cytotoxicity as quantified via the MTT assay up to the maximum imaging concentrations of 1 mg/mL, the Fc-HA-GQD formulation exhibits a higher cytotoxic response in the cancer cells (HeLa) targeted by the HA as opposed to healthy ones (HEK-293) that do not overexpress CD44, suggesting cancer-selective targeted efficacy. As Fc induces oxidative stress that is less mitigated in cancer cells, we expect it to also contribute to the observed cancer-selective treatment response. As a result, we propose Fc-HA-GQD formulation as a multifunctional targeted delivery, imaging, and cancer-specific treatment agent further to be studied in vivo.

Surface Plasmon Coupled Emission: a new super sensitive technique

Type: Graduate
Author(s): Luca Ceresa Physics & Astronomy
Advisor(s): Zygmunt Gryczynski Physics & Astronomy

Fluorescence has proved itself to be a useful tool in a wide variety of fields, ranging from environmental sensing to biomedical diagnostics. In this study, we propose to utilize a novel fluorescence-based technique called Surface Plasmon Coupled Emission (SPCE) to monitor molecular binding and to detect low concentrations of physiological markers (e.g. biomarkers present in the human body as a result of a disease). SPCE is characterized by directional emission that allows for a superior sensitivity and selectivity for detection. The development of an SPCE-based detection platform will allow for simple, fast and sensitive detection in a compact configuration that can be relatively easily implemented in the field or in primary care offices. Surface plasmon induced fluorescence at the interface of a thin metal layer (e.g. 50 nm of silver or gold) and a dielectric (e.g. glass) allows for highly enhanced excitation of fluorophores deposited on top of the metal film and very efficient detection due to the directional nature of this emission. As a result, we expect highly improved detection sensitivity compared to other fluorescence detection methods or other surface detection methods such as surface plasmon attenuated reflection (SPR).

Direct Excitation to the Triplet State: 5-Bromoindole

Type: Graduate
Author(s): Jose Chavez Physics & Astronomy Julian Borejdo Biology Luca Ceresa Physics & Astronomy Rafal Fudala Biology Ignacy Gryczynski Physics & Astronomy Joseph Kimball Physics & Astronomy Emma Kitchner Physics & Astronomy Tanya Shtoyko Chemistry & Biochemistry
Advisor(s): Zygmunt Gryczynski Physics & Astronomy

Tryptophan is one of the few amino acids that is intrinsically photoluminescent. This is because its side chain consists of indole. Indole’s photoluminescence has both fluorescence (emits for nanoseconds) and phosphorescence (emits for microseconds). Fluorescence emission comes from a singlet to singlet transition, while phosphorescence from a forbidden triplet to singlet transition. Taking advantage of tryptophan’s intrinsic emission, we can use it as a label-free probe for protein dynamics. For some of these dynamics, such as myosin binding to actin, the fluorescence lifetime of nanoseconds is too fast to monitor changes. The phosphorescence lifetime is much better suited to monitor these changes of large biomolecule interactions. Before any binding studies are developed, we have characterized the basic properties of indole’s phosphorescent properties. We began by embedding indole (as well as 5 – bromoindole) in a polymer matrix (PVA) to immobilize and thus increase the phosphorescence at room temperature. We discovered that using a longer wavelength of excitation (405 nm instead of 290 nm) we excite directly from the singlet state to the triplet state of indole, a typically forbidden process. This populates the triplet state without any transitions to the singlet state. This allows the polarization of phosphorescence emission to be preserved, and anisotropy measurements can be used to monitor biomolecular processes.

Using an agent-based model to explore the impact of inoculum dose and transmission mode on viral infection

Type: Graduate
Author(s): Baylor Fain Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy

In a virus study, the inoculum dose is the initial amount of virus used. It is correlated to the initial
amount of cells that become infected at the start of the study and thereby also correlated with the
amount of virus that will be produced by infected cells at the beginning of that study. Those virus spread
through a body in two known ways: cell free transmission and cell to cell transmission. While previous
research has investigated viruses based on free cell transmission, few models have incorporated cell to
cell transmission leading to unclear results and bias to certain variables. This research accounts for both
modes of transmission, using an agent-based framework, and varies the initial amount of virus, to
understand how inoculum dose affects the two transmission modes. Utilizing parallel processing, the
model represents virus infection and spread in a two-dimensional layer of cells in order to generate total
virus over time graphs for corresponding initial amount of virus. This project demonstrates how a
combination of agent-based models and parallel processing can allow researchers to perform the rapid
and large simulations necessary for viral dynamics research efficiently and affordably.

Utilizing Bogoliubov Transformations to Improve Accuracy in Computing Eigenvalues of Perturbed Harmonic Oscillators

Type: Graduate
Author(s): Carson Huey-You Physics & Astronomy
Advisor(s): Magnus Rittby Physics & Astronomy

In order to calculate the ground and excited states of a perturbed harmonic oscillator, we use computer codes developed from the results of coupled cluster techniques. More specifically, we have implemented a diagrammatic approach in order to efficiently derive cluster amplitude and energy equations, along with iterative Bogoliubov transformations in order to improve the accuracy of computed energies. Such Bogoliubov transformations improve the zeroth order Hamiltonian, which is shown for a quadratic and quartic perturbation. These results are then compared to exact results obtained from numerical integration of the Schrödinger equation, though we note that numerical integration cannot be performed for more complex systems of coupled harmonic oscillators under perturbation. Explicit coupled cluster equations are also presented for such coupled systems subjected to similar perturbations.

Multi-Swabbing the Deck

Type: Graduate
Author(s): Emma Kitchner Physics & Astronomy Luca Ceresa Physics & Astronomy Jose Chavez Physics & Astronomy
Advisor(s): Karol Gryczynski Physics & Astronomy

DNA biomarkers are of growing significance for the personalized medicine, with applications including diagnosis, prognosis, and determination of targeted therapies. However, even unicellular organisms can represent a heterogenous system on a molecular level. Improving the detection limits for low DNA concentrations will allow for better decision making, e.g., in clinical medicine, research endeavors, and human identification in forensic investigations where frequently only a minute amount of evidence material is available.
The first step for DNA collection is typically collecting specimen by specialized medical swabs. Medical swabs come in all different materials, shapes and sizes. They are not the same, but they are often used interchangeably. For DNA testing swabs can be used in buccal and surface swabbing for DNA. Then the swab with DNA on it is sent for analysis. A common analysis technique is using fluorescence. But what if the swab itself has some fluorescence? Do different types of swabs have different fluorescence? We want to test the inherent fluorescence of a variety of different types and brands of medical swabs to determine the kind with the best properties for highly sensitive DNA detection. If the swab’s fluorescence is short-lived, we expect that we will be able to separate out the swab’s signal from the DNA’s signal by using long-lived dyes and our novel multipulse excitation scheme.

Investigating Modulation of Graphene Oxide Fluorescence via External Electric Fields

Type: Graduate
Author(s): Bong Han Lee Physics & Astronomy Fabian Grote Physics & Astronomy Thomas Paz Physics & Astronomy Conor Ryan Physics & Astronomy Alina Valimukhametova Physics & Astronomy
Advisor(s): Anton V. Naumov Physics & Astronomy

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in nanodevices such as bio and gas sensors, solid state supercapacitors and solar cells. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to allow fine-tuning of its optical properties in the device geometry, new physical techniques are required that unlike existing chemical approaches yield substantial alteration of GO structure. Such desired new technique is one that is electronically-controlled and lead to reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modelling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/PVP films with up to 6% reversible decrease under 1.6 V/µm electric fields. On an individual flake level, a more substantial over 50% quenching is achieved for select GO flakes in polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modelled on a single exciton level by utilizing WKB approximation for electron escape form the exciton potential well. In an aqueous suspension at low fields GO flakes exhibit electrophoretic migration indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.

63andMe: A Genetic History of the Milky Way

Type: Graduate
Author(s): Amy Ray Physics & Astronomy John Donor Physics & Astronomy
Advisor(s): Peter Frinchaboy Physics & Astronomy

Star clusters are key age-dateable tracers of the chemical history of the Milky Way. Star clusters can provide significant constraints on galaxy chemical evolution models. The large discrepancies between different small studies limit the accuracy of these constraints, so a large uniform study is needed. To create a large uniform sample, we observed stars in 63 clusters with the same telescope. We then determined the chemical makeup of these stars using a machine learning tool called The Cannon. Using this sample, we examine the change in chemical abundance over the radius of our galaxy.

Interactions Between Microcrystalline ZnO and Extracellular Material of Staphylococcus Aureus

Type: Graduate
Author(s): John Reeks Physics & Astronomy Iman Ali Biology Jacob Tzoka Physics & Astronomy
Advisor(s): Yuri Strzhemechny Physics & Astronomy

Nano- and microcrystalline ZnO is a low-cost material, employed in many applications due to its optoelectronic, structural and chemical properties as well as a great variety of synthesis methods. Among these applications, antibacterial action of ZnO is a budding field of interdisciplinary research. Despite numerous studies of this antibacterial action, the physical and chemical mechanisms behind it are still largely not understood. In particular, the influence of the crystal surface morphology and surface-surface interactions between the bacteria and ZnO are largely unknown. Hexagonal (wurtzite) ZnO crystals terminate with three different types of crystallographic surfaces: charged polar hexagonal (Zn or O), electrically neutral nonpolar rectangular and partially polar pyramidal slanted. In our studies we employ a hydrothermal growth procedure to synthesize nanocrystals and microcrystals of ZnO with tunable morphology to investigate the influence of surface types on interactions with bacteria as well as surface charge dynamics. To quantify the antibacterial action we employ minimum inhibitory concentration (MIC) assays of staphylococcus aureus with hydrothermally-grown ZnO microcrystals. Scanning electron microscopy (SEM) is used to characterize the morphology of the as-grown ZnO specimens as well as the organization of these particles after their interactions with bacteria. To characterize electronic structure and dominant charge transport mechanisms at ZnO surfaces we performed photovoltage (SPV) experiments. Our results confirm that antibacterial action is a result of ZnO surface interactions with extracellular material, whereas internalization of ZnO particles (happening in the case of nanoscale ZnO) is not necessary for inhibition. We also report that the electronic transitions at the surface of the ZnO particles are consistent the theoretically predicted electronic structure of ZnO, with the spectral signatures of surface states which could be the source of the antimicrobial action.