Dwarf galaxies are the building blocks larger galaxies. Their shallow gravitational potentials makes them extremely sensitive to explosions of stars. To understand how dwarf galaxies form and evolve, we must study their formation, evolution and fate in a range of environments. Located 13 million light years away, Centaurus A is the closest massive elliptical galaxy making it ideal for investigating the effects of local environment on the formation and evolution of dwarf galaxy populations. We model the dwarf satellite populations of Centaurus using a suite of high resolution N-body simulations and the semi-analytic model (SAM) Galacticus (Benson, 2010). We determine the best fit parameters for well studied Milky Way satellite, before applying those parameters to generate simulated satellites around our Centaurus A's analog. Given the relatively low computational cost of N-body simulations and SAMs, we are able to explore the effects of uncertainties in the Centaurus A system, including its relatively unconstrained mass. Here we present initial results from our study for the first Centaurus A like galaxy.

Fifty percent of stars in the night sky are actually binary star systems, but finding and characterizing them requires significant data, time, and analysis. Studying the brighter star of the pair is fairly straightforward, but the secondary is commonly hidden. Using the infrared spectroscopy data from the Sloan Digital Sky Survey combined with the WIYN Open Cluster Survey, we create a longer baseline with which we can better characterize these stars. The Joker, a new Monte Carlo analysis technique, will help us reveal the hidden binary stars by producing solutions for the orbits of the systems. By finding new binary stars, we can better understand the demographics and composition of our chosen star cluster, NGC 6819, and also learn more about each individual companion of the systems.

During the first 100 million years after the Big Bang the universe was dark, and possibly full of terrors. Sometime during the first 500 million years, these cosmic dark ages ended with the ignition of the first stars. The first stars, which we call these Population III, contained only the hydrogen and helium formed in the Big Bang. These stars are interesting because they are thought to have started a domino effect of enrichment of elements heavier than helium through the cosmos. These ”heavier” elements formed in the core of stars are referred to in astronomy as ”metals”. Without ”metals” the gas out of which Population III stars form cools inefficiently, producing stars with masses as high as a few 1000 times the mass of our Sun. However, while we know that Population III stars are massive, we do not know exactly how massive as they are too faint for detection by all current and upcoming astronomy observatories. The work presented on this poster will explore one possible alternate avenue to answer the question: how massive were the first stars? As a result of their extreme masses, the most massive Population III stars will collapse directly into black holes with masses of a few hundred to a few thousand times the mass of our sun. A billion years after the Big Bang, as the era of the Population III stars ends, astronomers have observed the distribution of supermassive black holes (a million to a billion times the mass of the sun) in galaxies. Our work traces the evolution of the direct collapse black holes, formed from Population III stars, to determine whether the distribution of the masses of Population III stars left an imprint on the distribution of supermassive black holes, 500 million years later. The goal of this work is to randomly populate different potential distributions of Population III masses to compare the varying distributions of direct collapse black holes at different times. The result of this will eventually provide predictions for the dependence of the distribution of supermassive black holes, a billion years after the Big Bang, on the distribution of the masses of Population III stars.

Dark Matter (DM) is hypothesized to be an exotic particle that is invisible to human observation. But thankfully, its existence is proven through its gravitational interaction with luminous matter (such as stars and galaxies), and it is responsible for the formation of the humongous structures across our universe. The leading interpretation of DM is what we call Cold Dark Matter (CDM), where the DM particles have relatively low velocities and low energies. This causes structures to form quite quickly and easily in the early universe. While CDM can explain many observed properties of the universe, it is not without its flaws (specifically on the scale of low-mass dwarf galaxies). The hypothesis of Warm Dark Matter (WDM) poses a viable solution to the shortcomings of CDM. In WDM, the DM particles are of higher energy and have higher velocities. This would cause the formation of the first gravitationally bound structures in the Universe to be delayed when compared to CDM. Using a model to approximate varying temperatures of DM, we compare the rates and characteristics of early structure formation for the current CDM hypothesis, and that of many other types/temperatures of WDM. We expect that the differences between CDM and WDM will be most apparent during the first billion years after the Big Bang, just as the first stars in the Universe ignite. These results may be indicative of the true nature of dark matter, and finally bring our understanding into the light.

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. Thus, our work utilizes nitrogen-doped GQDs as a basis for targeted image-guided cancer therapy. GQDs serve 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 treatment. 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.

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 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).

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.

Driving through the disk of the Milky Way galaxy resides a gaseous stream that is associated with the Magellanic Clouds galaxies called the Leading Arm. The Milky Way will capture this stream of gas torn from the Magellanic Clouds to supply our galaxy with material to make future stars and planets. We study this gas cloud using Hubble Space Telescope observations to determine the complex's physical properties, such as the motion, temperature, ionization fraction, density, and total mass of the gas. With this observational data, we run computer simulations created with the Cloudy software to constrain these properties better. Measured ionization ratios and column densities from the Hubble observations act as inputs for our models. Studying these properties will better depict the processes that affect the stream of gas falling onto our galaxy's disk.

In this research we developed biocompatible Graphene Quantum Dots (GQDs) capable of emitting light in the infrared part of the light spectrum. Using the bottom up and top down approaches, we synthesized near-infrared light-emitting GQDs to be used for further cell studies as imaging and drug delivery agents for cancer detection and treatment.
From our bottom up approach, using a one-step hydrothermal reaction using a microwave and oven, the GQDs derived from the Glucose and Liquid ammonia mixture and those from from the L-glutamic acid showed near-infrared emission. And from our top down approach, using a UV based photolytic reaction, the GQDs derived from the mixture of urea, citric acid and hydrogen peroxide also showed near-infrared emission.

Type Ia Supernovae (SNe Ia) are used as measuring sticks in the structure of the Universe. These catastrophic explosions occur when two stars collide, but it’s unknown what kind of stars are combined to produce a SN Ia. Target 1 in our study is an unusual SN Ia; while a standard SN Ia would grow much dimmer after 300 days (late-time), this one remains bright. This is due to delayed interaction between the material ejected from the SN explosion colliding with the material in the surrounding region, causing light-curves to stagnate in late-time and be brighter than standard SNe Ia. It’s unknown if SNe like Target 1 are rare, but their properties would greatly aid in mapping the Universe. Therefore, we searched the public data from the Zwicky Transient Facility for more these types of SNe. We obtained 40 light-curves that are representative of the intrinsic SN Ia distribution in the nearby universe and found two instances of Target 1-like SNe.

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 “heavy” elements, including 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 in which the entire star blows itself apart [and fling], flinging “heavy” elements into the Universe. However, what will the detection, or non-detection of a PISN tell us about the nature of the first stars? To answer this question, we need to fully explore the range of mass distribution of Population III stars to determine the physics which governed Cosmic Dawn. We present results from a new model which treats the distribution of Population III masses as free parameters. In this work, we attempt to determine whether the masses of the first stars can be constrained given various possible observational results from JWST.

The debate surrounding the fundamental mechanisms behind the antibacterial action of ZnO has led to increased interest in the impact of surface interactions on this behavior. In this regard, the impact of the different polar vs. non-polar surfaces of the anisotropic wurtzite ZnO crystal lattice are of particular interest. For this purpose, we developed a hydrothermal growth method that allows us to produce microscale ZnO crystals of tunable morphology with varying relative abundances of surfaces with desired polarities. The micron scale of the obtained crystals is critical to avoid internalization by bacteria as a means to isolate effects related to surface interactions. Simultaneously, at this scale, the high surface-to-volume ratio leads surface interactions to dominate, resulting in surface and near-surface defect states to become highly influential on this behavior. Photoluminescence is a powerful, non-destructive tool for characterizing the electronic structure of a material allowing us to observe the nature of the defect states present in our samples. Photoluminescence measurements were made over a range of temperatures for both predominantly polar and non-polar morphologies. Results of these investigations have allowed us to describe the electronic structure of these microcrystals. We show that both the nature and density of surface defects states are significantly impacted by the relative abundance of polar and non-polar surfaces.

Photothermal Therapy (PTT) provides a promising new method of therapy for various medical conditions, including cancer, using infrared wavelengths. In my project, the photothermal effect of various nanomaterials—including Reduced Graphene Oxide, gold nanospheres and nanorods, and Copper Sulfide (CuS) nanoparticles—is characterized by irradiation of the aqueous materials with near-infrared radiation. These materials were then irradiated in live cell cultures to characterize their potential use as a treatment candidate.

Graphene quantum dots (GQDs) are unique derivatives of graphene that show promise in multiple biomedical applications as biosensors, bioimaging agents, and drug/gene delivery vehicles. Their ease in functionalization, biocompatibility, and intrinsic fluorescence enable those modalities. However, GQDs lack deep tissue magnetic resonance imaging (MRI) capabilities desirable for diagnostics. Considering that the drawbacks of MRI contrast agent toxicity are still poorly addressed, we develop novel Mn2+ or Gd3+ doped nitrogen-containing graphene quantum dots (NGQDs) to equip the GQDs with MRI capabilities and at the same time render contrast agents biocompatible. Water-soluble biocompatible Mn-NGQDs and Gd-NGQDs synthesized via single-step microwave-assisted scalable hydrothermal reaction enable dual MRI and fluorescence modalities. These quasi-spherical 3.9-6.6 nm average-sized structures possess highly crystalline graphitic lattice structure with 0.24 and 0.53 atomic % for Mn2+ and Gd3+ doping. This structure ensures high in vitro biocompatibility of up to 1.3 mg ml-1 and 1.5 mg ml-1 for Mn-NGQDs and Gd-NGQDs, respectively, and effective internalization in HEK-293 cells traced by intrinsic NGQD fluorescence. As MRI contrast agents with considerably low Gd and Mn content, Mn-NGQDs exhibit substantial transverse/longitudinal relaxivity (r 2/r 1) ratios of 11.190, showing potential as dual-mode longitudinal or transverse relaxation time (T 1 or T 2) contrast agents, while Gd-NGQDs possess r 2/r 1 of 1.148 with high r 1 of 9.546 mM-1 s-1 compared to commercial contrast agents, suggesting their potential as T1 contrast agents. Compared to other nanoplatforms, these novel Mn2+ and Gd3+ doped NGQDs not only provide scalable biocompatible alternatives as T1/T2 and T1 contrast agents but also enable in vitro intrinsic fluorescence imaging.

Many cancers are characterized by rapid cell growth and division. This growth causes the area to become densely packed, forming tumors and therefore limiting oxygen penetration, and also causing the cell to have elevated energy needs. These factors trigger the use of mechanisms which have a high acidic output, which makes cancerous environments measurably more acidic than their healthy counterparts. This study was conducted to determine the suitability of various nanomaterial-based platforms for pH sensing as an additive to their previously shown suitability for drug/gene delivery and bioimaging. Several platforms were chosen, including Glucose-Doped Graphene Quantum Dots (GGQDs), Reduced Graphene Oxide-Derived Graphene Quantum Dots (RGQDs), and Aluminum-Doped Reduced Graphene Oxide-Derived Graphene Quantum Dots (Al-RGQDs), which all have peaks in their emission spectra in both the visible and infrared range. 9 spectra were taken from each of these platforms in the visible and infrared ranges from pH 6.00 to 8.00, as would be expected in cancerous and healthy biological systems. These spectra were then analyzed for defining characteristics which would distinguish between the various pH levels. While the results from GGQDs and RGQDs are thus far inconclusive, the relative peak intensity readings from the visible and infrared Al-RGQDs showed a promising inverse relationship that bears further investigation.

Hydrogen energy is the most sustainable source of energy known to man. Though Earth has a seemingly limitless supply of hydrogen trapped in water molecules, industrial size production and storage of it has remained costly and dangerous. Reduced graphene oxide (rGO) shows great potential as a storage vessel for hydrogen while acting as a “catchers’ glove” for hydrogen when it is split from water. Where others have tried to store hydrogen in rGO by having it surrounded by hydrogen gas, I will attempt to directly attract hydrogen to rGO by taking advantage of hydrogen’s electrical attraction to rGO once it is split from water via electrolysis. This technique, paired with a novel method of preparation of the working cathode , could increase hydrogen storage in rGO that has not been achieved; furthering its potential as a safe, cost effective, and reversible hydrogen storage vessel.

Star clusters have been incredibly useful tools for studying the history of the Milky Way because they allow us to determine relative ages based on their chemical abundances. However, most stars are not in clusters, and current methods used to determine ages for individual stars produce substantial uncertainties. A new age method enabled by the precise photometry data of the NASA Kepler satellite is asteroseismology. Asteroseismology allows us to probe the internal structure of stars that are affected by age and composition. This research aims to calibrate the relationships between age, chemical abundances, and asteroseismology by analyzing data of stars in star clusters, which provide an independent measure of the stars' ages. This project aims to expand upon the currently used age and chemical abundance range and triple the number of open star clusters used to calibrate the asteroseismic age-mass-chemical abundance relation. We have combined asteroseismology data for stars in clusters within the Kepler 2 campaign fields with uniformly determined follow-up spectroscopic abundances from observations from the MMT.

Micro- and nano-scale ZnO particles are known to inhibit the growth of bacteria. Though this phenomenon has been vigorously studied, the fundamental mechanisms driving this action remain unknown. Mechanisms proposed by other studies include: the production of reactive oxide species, release of zinc ions, damage to the cell wall due to interactions with ZnO surfaces, and the inhibition of enzymes. ZnO surface defects serve as reaction sites for the processes driving these bactericidal interactions. Additionally, through MIC assays, we found antibacterial action of microparticles to be comparable to that of nanoscale particles. This confirms that antibacterial action of ZnO is rooted in surface-surface interactions between bacteria and ZnO. Therefore, our studies focus on ZnO surface charge dynamics and surface defects using surface photovoltage methods. Surface photovoltage experiments were performed on commercial grade ZnO nanoparticles and hydrothermally grown ZnO microcrystals in conjunction with antibacterial assays to elucidate the surface and near-surface charge dynamics associated with antibacterial processes of the ZnO surfaces.

The creation and evolution of elements, as a function of age, throughout the Milky Way disk provides a key constraint for galaxy evolution models. In an effort to provide these constraints, we have conducted an investigation into the rapid and slow-process neutron capture elemental abundances, which are created in supernovae, for a large sample of open clusters. Stars were identified as cluster members by the Open Cluster Chemical Abundance & Mapping (OCCAM) survey, which culls member candidates by Doppler velocity, metallicity, and proper motion from the observed OCCAM sample. We’ve obtained new data for neutron-capture elements in these clusters using the Subaru Observatory 8-m telescope in Hawaii with the High Dispersion Spectrograph (HDS). We are analyzing the neutron capture abundances in star clusters to measure the chemical evolution of the Milky Way.

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.

In recent times, nanomaterials have attracted interest in the scientific community due to their capacity for drug/gene delivery as well as their ability to target tissues and serve as probes for delivery pathways through various bioimaging approaches. Nanomaterial-based imaging systems in the near-infrared (NIR) region are desirable in vivo due to low biological autofluorescence, low tissue scattering, and increased penetration depth in animal tissue. However, low biocompatibility, as well as complexity in preparation, impede many current NIR imaging platforms from biomedical applications. In order to rectify this issue, we developed biocompatible NIR emitting graphene quantum dots (GQDs) and tested them for imaging in animal tissues. GQDs injected into mice intravenously through the tail vein show NIR emission in multiple organs including the intestine, kidney, spleen, and liver. Localization of both quantum dots in these organs was verified through the NIR fluorescence microscopy of organ slices, taken at multiple time points (1, 3, 6, 24 hours) via hyperspectral fluorescence microscopy. Slices in the 6 hour time point show the strongest fluorescence and characteristic GQD spectral signatures at ~950 nm compared to none in the control slices. These results indicate that GQDs show promising potential for future applications in theranostics, for instance as imaging or image-guided drug delivery agents.

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.

Fifty percent of stars in the night sky are actually binary star systems, but finding and characterizing them require significant data, time, and analysis. Studying the brighter star of the pair is fairly straightforward, but the secondary is commonly hidden. Using the infrared spectroscopy data from the Sloan Digital Sky Survey combined with The Joker, a new Monte Carlo analysis technique, we are working to reveal and characterize these hidden binary stars.

Previous reports show that it is not uncommon for patients to have two viruses at the same time. At the current time, we do not know how to treat co-infections. In order to test the effects of having these concurrent infections, we simulate the two infections using a mathematical model. We use our model to simulate influenza A virus co-infected with respiratory syncytial virus and parainfluenza virus co-infected with human rhinovirus. Using the model, we can estimate the co-duration of the viruses, the individual duration, and the peak virus amount for both viruses, both with and without drug treatment of the infections to figure out the best treatment strategies for co-infections. We find that sometimes treating one infection can lead to the lengthening of the other infection.

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.