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PHYS2020CHAVEZ14782 PHYS

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.

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PHYS2020FAIN39536 PHYS

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.

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PHYS2020HUEYYOU27370 PHYS

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.

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PHYS2020JESSIE17463 PHYS

Syncytia Virus Characteristics

Type: Undergraduate
Author(s): Benjamin Jessie Engineering
Advisor(s): Hana Dobrovolny Physics & Astronomy

Respiratory Syncytial Virus (RSV) is a common, contagious infection of the lungs and the respiratory tract. Syncytia are multinuclear cells that have fused together. It is so common that it effects all ages, but most people have experienced RSV by age two. Symptoms typically present similar to the common cold, with minimal effects and are easily treatable. RSV can, however, have detrimental effects on young children, the elderly, and those with compromised immune systems. As an individual infected cell can produce virus, so can syncytia cells. But, because of experimental limitations, it is difficult to measure characteristics such as viral production and lifespan of the syncytia cells. We will use mathematical models to study how different assumptions about the viral production and lifespan of syncytia change the resulting infection to determine whether less direct measurements can be used to determine syncytia viral production rates and lifespans.

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PHYS2020KITCHNER20551 PHYS

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.

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PHYS2020LEE3230 PHYS

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.

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PHYS2020MCCARTHY23828 PHYS

Quantifying rhinovirus infections using mathematical models

Type: Undergraduate
Author(s): Gabriel McCarthy Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy

Rhinovirus is the most prevalent virus in humans and is often the cause of the common cold. Modeling the dynamics of rhinovirus can allow us to observe important aspects of the virus including the general growth of the virus, the remaining target cells, the number of cells in the eclipse phase, and the number of infected cells. Following that, we can attempt to estimate parameters such as how much virus an infected cell produces or how long it takes an infected cell to start producing virus. We can use a method called Markov Chain Monte Carlo (MCMC) to try and gain more accurate estimates of those parameter based off observed data. Modeling rhinovirus will give us deeper insight into the workings of rhinovirus and allow us to try better and more accurate models of the virus.

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PHYS2020MCKINNEY21391 PHYS

Nitrogen-Doped Graphene Quantum Dots and Reduced Graphene Quantum Dots for Intensity Luminescence Nanothermometry

Type: Undergraduate
Author(s): Ryan McKinney Physics & Astronomy Bong Han Lee Physics & Astronomy
Advisor(s): Anton Naumov Physics & Astronomy

Non-invasive temperature sensing is necessary for the analysis of biological processes occurring in the human body including cellular enzyme activity, protein expression, and ion regulation. Considering that a variety of such biological processes occur at the microscopic scale, a mechanism allowing for the detection of the temperature changes in microscopic environments is desired. Although several such techniques have been developed involving nanomaterials, there is still a need in deterministic non-invasive biocompatible approach allowing for temperature measurements both outside the cells and in the intracellular compartments. Here we develop a novel approach utilizing graphene quantum dots (GQDs) as agents for such detection. Because of their small 2-5 nm size, non-invasive optical sensitivity to temperature change and high biocompatibility, GQDs enable biologically safe sub-cellular resolution imaging. Both bottom-up synthesized nitrogen-doped graphene quantum dots and quantum dots produced from reduced graphene oxide via top-down approach in this work exhibit temperature-induced fluorescence variations used as sensing mechanism. Distinctive quenching of quantum dot fluorescence by up to 19.8 % is observed, in a temperature range from 25℃ to 49℃, in aqueous solution, while the intensity is restored to the original values as the temperature decreases back to 25℃. A similar trend is observed in vitro in HeLa cells as the cellular temperature is increased from 25℃ to 41℃. Our findings suggest that the temperature-dependent fluorescence quenching of bottom-up and top-down-synthesized graphene quantum dots can serve as non-invasive reversible deterministic mechanism for temperature sensing in microscopic sub-cellular biological environments.

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PHYS2020RAY58064 PHYS

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.

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PHYS2020REEKS62679 PHYS

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.

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PHYS2020REEKS8931 PHYS

Role of Surface Charge Dynamics in UV-Induced Hydrophilic Flipping of Polysulfone Thin Films

Type: Graduate
Author(s): John Reeks Physics & Astronomy Pavan Ahluwalia Physics & Astronomy Edward Bormashenko Physics & Astronomy Luc Le Physics & Astronomy Logan Simon Physics & Astronomy
Advisor(s): Yuri Strzhemechny Physics & Astronomy

Reportedly, hydrophobic surfaces of polysulfone (PSu) thin films become hydrophilic following exposure to UV radiation and it can affect PSu novel applications in microfluidics and biophysics. Fundamental mechanisms behind this effect remain unknown. To elucidate them, in our work we study surface charge transport employing surface photovoltage (SPV) on thin PSu polysulfone films spin-cast on silicon substrates. Since exposure of PSu even to an ambient UV light could affect the surface properties we ran SPV spectroscopy as well as SPV transient experiments on both as-received samples fabricated in darkness and UV-irradiated films of varying and controllable thicknesses. We report on the comparison of the SPV response in the as-deposited and UV-irradiated polysulfone samples.

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PHYS2020SPOO57976 PHYS

​ Moving Towards a Better Kinematic Understanding of Our Milky Way ​ and its Stellar Populations

Type: Graduate
Author(s): Taylor Spoo Physics & Astronomy
Advisor(s): Peter Frinchaboy Physics & Astronomy Kenneth Carrell Physics & Astronomy

Modern astronomical catalogs consist of up to billions of stars and measure various properties of these objects. There have been recent data releases from two of these surveys, GAIA which measures positions and distances, and APOGEE which measures radial velocities and stellar physical properties. By combining these datasets we have the full 6D phase space information for each star and can compute orbital characteristics and kinematics properties. APOGEE targeted specific stellar populations in our Milky Way and determined some of their physical properties. By cross matching with GAIA, we are able to fully describe the orbits of these populations and look for potential new members that have the same physical and kinematic properties but are not located in the immediate vicinity. We will present kinematic properties of the full cross matched dataset as well as information on the targeted stellar populations of the Milky Way.

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PHYS2020VALIMUKHAMETOVA21642 PHYS

The Role of Graphene-Oxide in Stabilizing the Structure of the High-Temperature γ-Fe Phase

Type: Graduate
Author(s): Alina Valimukhametova Physics & Astronomy
Advisor(s): Anton Naumov Physics & Astronomy

Metal nanoparticles on a substrate have gained significant attention in recent years as novel systems for new generations of catalysts. Among other metals, iron attracts constant attention due to its low cost. Iron possess either the body-centered cubic (bcc) or the face-centered cubic (fcc) structure. Up to 917 °C, iron exists in its α-form (α-Fe) with the thermodynamically bcc lattice. At 917 °C, α-Fe transforms into the fcc lattice, and this allotrope is termed as γ-iron (γ-Fe) (austenite) with diamagnetic properties. According to the iron-carbon phase diagram, γ-Fe can incorporate up to 2.03% carbon. Lowering the temperature below 917 °C, carbon atoms diffuse out of the structure, and γ-Fe turns back to α-Fe. Up to now, γ-Fe could not be stabilized without such impurities as Mn, Cr, Ni at room temperature. We have obtained of iron nanoparticles with the face-centered cubic structure with diameters of up to 200 nm without impurities on the substrate of graphene oxide by thermal annealing in an inert gas. In our work we show that phases formation of iron depends on the temperature of annealing. At the annealing temperature from 300 ºC through 600 ºC only iron oxides are formed. We established the unexpected formation of the γ-phase already at 700°C by X-Ray diffraction and Mössbauer spectroscopy. These methods clearly identify the stability of the γ-phase at room temperature. The rather low transition temperature of α-Fe to γ-Fe already starting at 700 °C suggests that the mechanism for the transformation is different from that observed for bulk iron. The maximum γ-iron nanoparticles content on the substrate of graphene oxide was fixed at an annealing temperature of 950 °C.

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PHYS2019BUESCHEL12591 PHYS

Modeling of parvovirus treatment of cancer

Type: Undergraduate
Author(s): Devina Bueschel Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy
Location: Session: 2; 2nd Floor; Table Number: 4

presentation location

Rat Parvovirus is found in rat liver and can infect and cause changes in tumor cells. When tumor cells are infected, the cells can revert back to benign or uncancerous cells. We describe and analyze a mathematical model of infected and noninfected tumor cells when introduced to the parvovirus. Using nonlinear analysis, we find the conditions for cure of the tumor.

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PHYS2019CAMPBELL56087 PHYS

Graphene Quantum Dots as Imaging, Sensing, and Delivery Agents

Type: Graduate
Author(s): Elizabeth Campbell Physics & Astronomy Giridhar Akkaraju Biology Roberto Gonzalez-Rodriguez Chemistry & Biochemistry Md. Tanvir Hasan Physics & Astronomy
Advisor(s): Anton Naumov Physics & Astronomy
Location: Session: 2; Basement; Table Number: 10

presentation location

Graphene quantum dots (GQDs) are novel materials with a number of unique properties that can be applied in electronics, sensing and biotechnology. GQDs possess physical properties that are critical for biomedical applications, including small size (3-5 nm), high quantum yield, and pH-dependent fluorescence emission in the visible/near-infrared, providing a possibility of molecular imaging, and pH-sensing. They also show very low cytotoxicity suggesting high potential for multiple biomedical applications. GQDs can also be doped to form nitrogen doped graphene quantum dots (N-GQDs), sulfur doped graphene quantum dots (NS-GQDs) and boron nitrogen doped graphene quantum dots (BN-GQDs), which allow these optical properties to be adjusted. We utilize and modify these properties to yield a multifunctional delivery/imaging/sensing platform geared toward the analysis of cancer therapeutics delivery in vitro. In our work, we outline how GQDs can serve as potential drug transport agents and as molecular markers for imaging the delivery pathways. Optimal emission and excitation are selected for each quantum dot to minimize the autofluorescence of cells, allowing them to be imaged in vitro. Emission in healthy (HEK-293) and cancer (HeLa and MCF-7) cells is quantified for a variety of pH environments to identify the ideal conditions for cellular internalization and pH-sensing of acidic cancerous environments. In addition, in vitro fluorescence microscopy analysis provides quantitative assessment for accumulation in cells. The results of this work suggest GQDs as innovative and effective highly biocompatible multifunctional platforms for cancer therapeutics.

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PHYS2019CERESA50306 PHYS

How to deal with inner filter effect in fluorescence experiments

Type: Graduate
Author(s): Luca Ceresa Physics & Astronomy Jose Chavez Physics & Astronomy Ignacy Gryczynski Physics & Astronomy Joe Kimball Physics & Astronomy
Advisor(s): Zygmunt Gryczynski Physics & Astronomy
Location: Session: 1; 2nd Floor; Table Number: 2

presentation location

Fluorescence is a very useful and popular technique which has been used in a wide variety of fields and, of late most importantly, at the intersection of biophysics, biochemistry and medicine. Despite being relatively simple from a theoretical point of view, it turns out that practical applications can have trivial problems that can cause significant spectroscopic problems. Specifically, an often overlooked yet fundamental obstacle in fluorescence spectroscopy is the nonlinearity of fluorescence intensity versus fluorophore absorption. This is referred to as the inner-filter effect. In literature, it is divided into a “primary inner-filter effect” and a “secondary inner-filter effect”. The former is caused by the absorption of the excitation light, which results in the lowering of the intensity of light reaching deeper regions of the solution. The latter is represented by the reabsorption of the emitted fluorescence by the fluorophores in the solution. Due to the fact that the primary inner filter effect is a direct consequence of the high concentration of the solution, to observe the secondary inner filter effect it is necessary to have a chromophore which absorbs part of the light that is emitted by the main fluorophore. Although working with low concentrations is generally recognized as a good practice to avoid artifacts related to inner filter effects, the primary inner filter effect can occur even at low absorbances (< 0.05). Furthermore, it is possible that using solutions with high absorbance is strictly necessary in studying the photophysical properties of fluorescent dyes and the interactions of biological macromolecules. Therefore, a reliable correction method for inner filter effects is fundamental for spectroscopic studies. Since it has been reported that the existing methods for correcting the fluorescence intensity are hard to implement in practice, we propose a strategy based on the previous calculation of the so called “sensitivity factor” of a spectrofluorometer. By mounting a cuvette on a movable holder in a square geometry setup, we can modify the position of the cuvette during a regular emission/excitation experiment. This allows us to determine the sensitivity factor. This result can be effectively used to correct the emission/excitation spectra to restore the linearity between absorbance and fluorescence intensity in samples characterized by high concentrations.

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PHYS2019CHAVEZ34578 PHYS

Phosphorescence – Potential Biological Applications of Direct Excitation to the Triplet State.

Type: Graduate
Author(s): Jose Chavez Physics & Astronomy Luca Ceresa Physics & Astronomy Ignacy Gryczynski Physics & Astronomy Joe Kimball Physics & Astronomy
Advisor(s): Zygmunt Gryczynski Physics & Astronomy
Location: Session: 2; 3rd Floor; Table Number: 2

presentation location

Fluorescence has grown to be the most sensitive detection technique used in a variety of biophysical, biochemical and medical applications for several decades. However, there is an interesting luminescence similar to fluorescence which causes an “afterglow effect” (“glow in the dark”). This is called “phosphorescence”. Phosphorescence has an exceptionally longer lifetime (milli or microseconds) compared to fluorescence (nanoseconds). This can be up to a million times longer. Modern fluorescence lifetime measurements require sensitive detectors that cost several ten to hundreds of thousands of dollars, while a phosphorescence lifetime detector can be in the thousands range. This detector uses ocean optics spectrometry with a phosphoroscope to measure phosphorescence. With this application we want to use it for studying protein dynamics such as shape, spacing, binding, etc. The novelty for this approach is using tryptophan as a probe for direct excitation to the phosphorescence triplet state. This means the usual encounter of fluorescence there is a continuous light source. When exposed the sample will emit its fluorescence. Once removed from the light source, since fluorescence is so fast when decaying, will expire off. However, with phosphorescence, after the removal of the light source, the sample still emits. This procedure if successful will circumvent fluorescence and just achieve phosphorescence. To study this we will be using PVA (poly vinyl alcohol [plastic]) with 5,6 – Benzoquinoline, Indole, and Tryptophan where the first compound is confirmed to have phosphorescence able to be seen even with the naked eye at room temperature. These will be studied in a device that will measure phosphorescence called a fluorospectrometer (Varian Eclipse) and the phosphoroscope. With this information we can find out what color (wavelength) to excite the tryptophan and circumvent fluorescence to phosphorescence.

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PHYS2019CIAMPA28285 PHYS

Massive Winds Triggered by Supernovae in the Large Magellanic Cloud Galaxy

Type: Graduate
Author(s): Drew Ciampa Physics & Astronomy
Advisor(s): Kat Barger Physics & Astronomy
Location: Session: 1; Basement; Table Number: 6

presentation location

Massive amounts of gaseous material are being ejected from the nearby Large Magellanic Cloud (LMC) due to supernovae explosions occurring inside the galaxy. These explosions influence how gas cycles in and out of a galaxy and is crucial for our understanding of how galaxies evolve. Being the nearest gas-rich galaxy, the LMC provides us with an excellent opportunity to explore this gas cycle in detail. We have combined spectroscopically resolved observations to investigate the influence supernovae have on the LMC gas and the connection between supernovae explosions and the currently flowing galactic wind.

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PHYS2019DONOR55459 PHYS

Old Problems Require Modern Solutions: a Data-Driven Approach to Modeling Stellar Populations

Type: Graduate
Author(s): John Donor Physics & Astronomy John Wise Physics & Astronomy
Advisor(s): Peter Frinchaboy Physics & Astronomy
Location: Session: 2; Basement; Table Number: 7

presentation location

The problem of fitting isochrones, theoretical models of stellar populations, to the observed stellar populations (e.g. star clusters) has plagued observational astronomy for decades. A plethora of algorithms have been developed, but many fall short of their goals, and almost all are very computationally expensive. We present a new, computationally efficient technique made possible by first creating a fiducial representation of the data. This concise representation allows for a robust comparison to many theoretical models using a Markov-Chain Monte Carlo (MCMC) approach, quickly producing not only accurate fits but reasonable constraints on the final fitting parameters. The technique is applied to a number of star clusters, and the results are discussed in the context of Galactic chemical evolution.

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PHYS2019FAIN18003 PHYS

Investigating viral transmission using an agent based model

Type: Graduate
Author(s): Baylor Fain Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy
Location: Session: 2; 3rd Floor; Table Number: 7

presentation location

A virus spreads through a body in two known ways: free cell transmission and cell to cell transmission. During free cell transmission, cells make viruses that diffuse throughout the body which may cause any cell that the virus touches to become infected. During cell to cell transmission, a virus spreads to a neighboring cell through an intercellular transfer. 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 free cell and cell to cell transmission, using an agent-based framework. 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 dose of virus.

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PHYS2019HASAN44461 PHYS

Optical Properties Alteration and Photo-Voltaic Applications of Nitrogen-Doped Graphene Quantum Dots

Type: Graduate
Author(s): Md Tanvir Hasan Physics & Astronomy Roberto Gonzalez-Rodriguez Physics & Astronomy Conor Ryan Physics & Astronomy
Advisor(s): Anton Naumov Physics & Astronomy
Location: Session: 1; Basement; Table Number: 2

presentation location

In this work, a simple/scalable microwave-facilitated hydrothermal route is used to produce nitrogen self-doped graphene quantum dots (NGQDs) from a sole glucosamine precursor. These NGQDs with average sizes of ~6nm show bright/stable fluorescence both in the visible and near-IR. The structural and optical properties of as-prepared NGQDs are further altered to provide control for optoelectronic applications by using ozone and thermal treatment. Thermal processing serves as controllable avenues to decrease GQD emission via anticipated reduction processes. Oxidative ozone treatment results in the decrease of GQD average size down to 5.23 nm and a more disordered structure due to the introduction of the new functional groups. Structural and optical characterization was performed utilizing TEM, AFM, SEM microscopy and FTIR, EDX, Raman, fluorescence, absorbance spectroscopy. FTIR, EDX and Raman data suggest that this processing introduces oxygen-containing functional groups, enhancing the atomic percentage of oxygen and increasing ID/IG ratio. Ozone treatment shows enhancement of visible emission which is observed from 0 to 16 min ozone processing with following over oxidation-induced defect-related quenching. On the other hand, a progressive increase in defect-related NIR emission is observed up to 45 min. Such alteration of optoelectronic properties enhances NGQD performance in photovoltaic devices.

Untreated NGQDs (Un-NGQDs) and ozone-treated NGQDs (Oz-NGQDs) are utilized as a photoactive layer to fabricate a variety of solar cells. Although devices with untreated NGQDs show performances similar to existing reports, Oz-NGQDs exhibit significant improvement (~six fold) with maximum PCE of 2.64%, an open circuit voltage of ~0.83V, a short circuit current density of 4.8 mA/cm^2, and an excellent fill factor of ~86.4%. This enhancement can be potentially attributed to the increased/broadened visible absorption feature in device state due to the efficient charge transfer between the hole-blocking layer of TiO2 and Oz-NGQD having enhanced concentration of functional groups. This work suggests ozone treatment as an easy and powerful technique to alter the optoelectronic properties of versatile and scalably produced NGQDs which can be successfully utilized as an eco-friendly photoactive layer to boost the photovoltaic performance of solar cells.

(Presentation is private)

PHYS2019HUEYYOU48564 PHYS

Exploring a system of coupled quartic oscillators with coupled cluster methods

Type: Graduate
Author(s): Carson Huey-You Physics & Astronomy
Advisor(s): Magnus Rittby Physics & Astronomy
Location: Session: 1; Basement; Table Number: 7

presentation location

Quantum mechanical oscillations of a many-body system about a local potential minimum can in a first approximation be modeled by a set of harmonic oscillators about a local potential minimum. In more sophisticated models one also has to consider anharmonic effects.
Here we present the first steps towards a systematic solution of ground and excited state energies for a set of coupled quartic oscillators using coupled cluster techniques. We present the general approach of the equation of motion coupled cluster (EOM-CC) method. We give illustrative details of the diagrammatic approach to obtaining our operating equations as well as the resulting EOM-CC equations for a simple system of coupled harmonic oscillators perturbed by a quadratic perturbation. We point to the connection with Bogoliubov transformations and finally we illustrate the numerical behavior of the EOM-CC non-linear iterations and matrix diagonalization of our effective Hamiltonian obtained with our Python code.

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PHYS2019JHA46123 PHYS

Modeling polymerase inhibitor treatment of RSV

Type: Undergraduate
Author(s): Rashmi Jha Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy
Location: Session: 2; 2nd Floor; Table Number: 5

presentation location

Respiratory syncytial virus, or RSV, is a virus that commonly causes lower respiratory tract infections throughout childhood and infancy. Most people who contract the virus recover within a short period of time, but it can cause respiratory illness, hospitalization, and even death within infants and the elderly. Agents that can effectively combat RSV are still not available for widespread clinical use, but one of the targets being investigated is PC786, a novel inhaled L-protein polymerase inhibitor. Using data from previous publications, we created models of the relationship between volume of PC786 and viral load in patients with RSV to try to determine how to best model the action of this drug.

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PHYS2019LEE28437 PHYS

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
Location: Session: 1; Basement; Table Number: 5

presentation location

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.

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PHYS2019MCCARTHY57534 PHYS

Effect of the Hill coefficient on estimates of drug efficacy

Type: Undergraduate
Author(s): Gabriel McCarthy Physics & Astronomy
Advisor(s): Hana Dobrovolny Physics & Astronomy
Location: Session: 2; 2nd Floor; Table Number: 6

presentation location

We are modeling the effect of the Hill coefficient on the volume of a tumor. This is to test drugs that may bind to multiple receptors and compare them to each other. We are using Python and used 4 main parameters and one equation. We modeled the Volume and the Dose Response Curves as well as the Emax and Ic50. We used the different positive Hill Coefficients and studied the effect on dose and carrying capacity.

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