Physics Colloquium - Fall 2018

Speaker: Jonathan B. Chaires, James Graham Brown Cancer Center

Abstract: Telomerase reverse transcriptase (hTERT) is the catalytic subunit of the enzyme telomerase that is essential for the maintenance of telomeres, the protective end-capping structures of chromosomes. Expression of the gene that codes for hTERT is controlled by a promoter region that contains a sequence that potentially forms a four-stranded G-quadruplex structure, a novel DNA form distinct from the canonical and well-known duplex DNA first described by Watson and Crick. This seminar will describe our biophysical and biochemical studies aimed at defining the details of G-quadruplex structure. Supported by NIH grant GM 077422.

Speaker: Herbert Malphrus, Morehead State University

Abstract: The Lunar IceCube mission is designed to prospect for water ice and other lunar volatiles from lunar orbit. Morehead State University is leading the mission in partnership with NASA Goddard Spaceflight Center, JPL, Busek and Vermont Tech. It was slected under NASA’s NextSTEP program and will fly on Exploration Mission-1 in 2019.Lunar IceCube, a 6U CubeSat designed to prospect for water in solid, liquid, and vapor forms and other volatiles from a low-perigee, highly inclined lunar orbit, has been selected by NASA to fly on Exploration Mission -1 (EM-1). The mission is a partnership between Morehead State University, NASA Goddard Spaceflight Center, JPL, and the Busek Space Propulsion Company. Lunar IceCube will be deployed during lunar trajectory by the Space Launch System (SLS) and use an innovative RF Ion engine to achieve lunar capture and the science orbit (inertially locked, highly elliptical, 100 km periapsis) to investigate the distribution of water as a function of time of day, latitude, and regolith composition in the context of lunar mineralogy. Lunar IceCube will include the Broadband InfraRed Compact High Resolution Exploration Spectrometer (BIRCHES), developed by GSFC- a compact version of the successful New Horizons instrument designed with the high spectral resolution (5 nm) and wavelength range (1 to 4 μm) needed to distinguish forms of water, including ice. The mission will complement the scientific work of other missions by focusing on the abundance, location and transportation physics of water ice on the lunar surface at a variety of latitudes. Lunar IceCube, while primarily a science mission, will demonstrate technologies that will enable future interplanetary exploration with small satellite platforms including radiation-hardened subsystems, a precise ranging transponder/transceiver, a capable attitude determination and control system, a high power solar array and an innovative electric propulsion system (EP). The EP (Busek BIT-3 Iodine engine) generates 1.2km-1 of delta-v and, combined with an innovative low energy manifold trajectory, allows the spacecraft to reach lunar orbit from Earth escape with minimal energy. The 13 secondary payloads to be deployed on EM-1, including Lunar IceCube, will usher in a new era of solar system exploration with small satellite platforms. The presentation will discuss challenges and solutions related to interplanetary smallsat development and mission formulation. Also to be discussed are potential opportunities for students in the Master of Science in Space Systems Engineering program at Morehead State University and potential research collaborations.

Speaker: Dr. Narayanan, University of Louisville Mechanical Engineering

Abstract: Lithium-sulfur (Li-S) batteries hold tremendous promise in electric transportation owing to their high theoretical specific energy and low-cost of sulfur. However, techno-economic studies show that they need to operate under lean-electrolyte conditions (low electrolyte-to-sulfur ratio E/S<1 mL/g) to compete effectively with existing Li-ion technology. Developing long-lived Li-S batteries with high capacity at low E/S ratio has remained extremely challenging owing to (a) reliance of traditional Li-S chemistry on large excess of electrolytes (>10 mg/L) to solubilize the intermediate lithium polysulfide reaction products, and (b) uncontrolled parasitic reactions at the Li-anode. In this seminar, I will demonstrate that an emerging class of electrolytes containing high concentration of Li-salts (called sparingly solvating electrolytes, SSE in short) could provide a way to mitigate these longstanding challenges. Using first-principles molecular dynamics simulations, and quantum chemical calculations, we find that within a SSE, the local solvation structure around Li+ ion, and long-range electrolyte structure can be precisely controlled by varying composition of the electrolyte. In combination with electrochemical experiments and spectroscopic measurements, our computations show that extended network structures can be engineered within a SSE by optimizing its composition. These network structures facilitate a quasi-solid-state speciation pathway that enables low E/S operation, while simultaneously inhibiting parasitic reactions at the anode. I will discuss these results in the context of designing electrolytes for long-lived, stable, and high-energy density Li-S batteries.

Speaker: Shannon McKenzie, Johns Hopkins University

Abstract: Life on Earth seems to require three key ingredients: carbon, water, and energy. In this talk, I will discuss the evidence from the Cassini-Huygens mission for each of these factors at Saturn's largest moon, Titan. Photochemistry in the atmosphere creates haze particles of complex hydrocarbons that obscure the surface in most of the visible and much of the near infrared. These haze particles can be up to the size of DNA and protein molecules found on Earth. Additionally, methane (CH4) plays the same role on Titan that water does on Earth, raining down out of the atmosphere to pool on the surface before evaporating back into the atmosphere. Titan has a subsurface ocean--like other icy satellites Encealdus, Europa, and Ganymede--hidden by a crust of water ice. In order to evaluate the habitability of Titan and explore the bounds of prebiotic chemistry, we need to go back and sample the diversity of materials on Titan's surface and understand how processes at the surface modify the photochemical products that fallout from the atmosphere. Dragonfly, a mission concept is currently in competition in NASA's New Frontier's program, is designed to do exactly that.

Speaker: Amanda Moffett, Vanderbilt University / GAMA Collaboration

Abstract: Observations of galaxies outside our own Milky Way have provided a remarkable number of important insights into the fundamental physical processes governing the universe. In the first part of this talk, I will introduce our current model for the growth of structure and the hierarchical build up of galaxies over cosmic time. I will then discuss observational evidence supporting this model along with some outstanding challenges, including the puzzling abundance of disk galaxy populations in the local universe and the “missing mass” problems probed by galaxy surveys. I next discuss my research focused on identifying observational evidence for the theorized process of galaxy disk regrowth after destructive mergers and on measuring the balance of galaxy mass assembled through violent mergers versus quiescent growth. Finally, I discuss ongoing work aimed at constraining models for the build up of metals in galaxies through measurement of the galaxy metallicity distribution in a survey volume that reaches dwarf galaxy masses.

Speaker: Edward W. (Rocky) Kolb, University of Chicago

Abstract: The big bang is a laboratory to explore the properties of particles that cannot be explored at terrestrial laboratories. In addition to thermal production of new particles, there is another source of cosmological particle production. In 1939 Edwin Schrödinger pointed out that particle-antiparticle pairs could be created merely by the violent expansion of space. The spontaneous appearance of particles from the vacuum so disturbed Schrödinger that he referred to it as an "alarming phenomenon." The phenomenon is now thought to be the origin of density fluctuations produced in inflation as well as a background of gravitational waves. Gravitational particle production is a rich phenomenon, which continues to be explored.

Speaker: Sathitsuksanoh Noppadon, University of Lousiville, Speed School

Abstract: Industrial hemp, a variety of the Cannabis sativa and the same plant species as marijuana, has been of interests as a potential renewable feedstock in recent years because every part of hemp can be used to produce a variety of industrial products. For example, its outer shell (bast) can be used to make fibers for textiles. Its flowering materials (e.g., flowers and leaves) are good sources for high-valued cannabidiol (CBD) oil, which can be extracted and used in medical applications. The hemp oil can be extracted from seeds for cooking and cosmetics. Although hemp has numerous potential applications, it is one of the most controversial plants by law and by perception, limiting research being done on. Understanding hemp genetics, potential hemp processing strategies, and challenges in hemp research is important not only to advance scientific knowledge but also to promote the public understanding of this misunderstood plant. This talk aims to bridge between the chemical structure of hemp and its applications by highlighting how spectroscopies can lead to designing catalysts for hemp upgrading.

Speaker: Benne Holwerda, University of Louisville, Department of Physics & Astronomy

Abstract: We report the recovery of parts of the streams in Hubble Space Telescope Advanced Camera for Surveys and Wide-Field Camera 3 (HST ACS & WFC3) observations, using Red Giant Branch stars surrounding NGC 891, at ~600" and ~300" (27 and 13 kpc) from the nucleus on the major and minor axes respectively. The stellar stream does not contain young stars (<1Gyr), and the RGB population is consistent with a metallicity of [Fe/H] ~ -0.8dex, similar to earlier estimates for the combined streams surrounding NGC 891. We argue that the spatial overlap between the major axis stellar stream in the HST observations and a known counter-rotating HI (atomic hydrogen) complex is likely a coincidence or a projection effect. The color-magnitude diagram of stars within this HI complex reveals no recent (massive) star formation.

Here, we argue that the stellar streams surrounding NGC 891 and the extra-planar gas all originate from a single encounter. The similar metallicity at both major and minor intersections implies the streams have a common origin. Both the metallicity and the stream geometry imply a stellar mass of M_* ~ 10⁹ M_☉ satellite. The implied elapsed accretion time from the geometry is 1.5 Gyr. Assuming a typical gas-to-stellar ratios of unity for a late-type galaxies of this stellar mass, the implied HI accretion rate is around 1 M_☉/yr where the current several 10⁷ M_☉ cold extra-planar gas could represent the last few percent of accretion with most of the accreted gas already assimilated by NGC 891 or its halo. Both timescale and proximity argue against the extra-planar HI originating from interaction with UGC 1807. This finding has implications for how Milky Way like galaxies get their fuel; not through cold streams from pristine gas outside but the slow ingestion of a LMC-like galaxy.