Physics Colloquium - Spring 2017

Speaker: Blakesley Burkhart, Harvard-Smithsonian Center for Astrophysics

Abstract: Dr. Blakesley Burkhart is currently an Einstein Fellow and joint ITC/SMA Fellow at the Harvard-Smithsonian Center for Astrophysics in the Institute for Theory and Computation (ITC). She received her MS and Ph.D. in Physics from the University of Wisconsin-Madison and graduated Magna Cum Laude from the University of Louisville with a B.S. in Physics & Math in 2008.

Speaker: Dale Schaefer, University of Cincinnati

Abstract: In the last decade nanotalk has invaded science and engineering as well as popular culture–nanomedicine, nanomaterials, nanobuckets, nanoreactors, nanobots. But what is nature like at the nanometer level? Unfortunately simplified schematics (cartoons) have displaced quantitative morphological characterization so we actually don’t know. Given our natural impose order on nature cartoons often fail to capture nature’s complexity. This presentation will examine several case studies where conceptual simplification has led not only to misunderstanding, but also to bad investments. Small angle scattering and reflectivity are used to examine the morphology of nanocomposites and nanostructured interfaces. In the cases of nanocomposites, the intrinsic flexibility of carbon nanotubes drastically reduces the reinforcing effect. Interfaces, on the other hand are seldom simple multilayered structures, which impacts the development of many technologies from coatings to biomaterials.

Dale W. Schaefer is Professor of Chemical and Materials Engineering at the University of Cincinnati. He received his PhD in Physical Chemistry at MIT and did post doctoral studies in the Department of Physics at MIT. Dr. Schaefer previously served as a technical manager at Sandia National Laboratories, a Senior Technical Advisor at the Department of Energy and as Dean of Engineering at the University of Cincinnati. He is a Fellow of the American Physical Society and the American Institute of Chemists. In 2004 he was the John Wheatley Scholar at Los Alamos National Laboratory. He was a visiting scientist at the Chinese Academy of Sciences (2005, 2007). He is a specialist on structure-property relationships in soft materials, which he studies by scattering methods. His most recent projects include chem-bio resistant membranes, silane protective films, alcohol perception, responsive interfaces and colloids for consumer products. He is the author of 150 refereed journal publications with an h-impact factor of 53.

Speaker: G.P. Das, Indian Cultivation of Science, Calcutta

Abstract: Prof. G.P. Das is a condensed matter physicist and a materials scientist working as a senior professor in the Indian Association for the Cultivation of Science (IACS) in Kolkata. His research interests span a wide cross-section encompassing electronic structure and properties of various kinds of alloys, interfaces, clusters, and nanostructured materials. He has been working on hydrogen storage materials, spintronics materials, and 2-dimensional nanostructures beyond graphene. He has authored and co-authored more than 150 research publications in peer reviewed journals, book chapters etc. Prof. Das served as visiting scientist in Max Planck Institute Stuttgart (Germany), Virginia Commonwealth University, Richmond (USA), Institute of Materials Research, Sendai (Japan). He has spearheaded a number of national and international programmes and initiatives, such as the Asian Consortium for Computational Materials Science (ACCMS), Asian Hydrogen Storage Initiative, a Coordinated Research Programme on Spintronics materials etc. He is recipient of several awards, including the ACCMS award in 2013 and the Materials Research Society (MRSI) silver jubilee award in 2014.

Speaker: A. Seo, University of Kentucky

Abstract: One-dimensional (1D) systems offer a useful platform for studying low-dimensional phenomena often associated with the onset of critical quantum phase transitions. While exactly solvable models, such as Luttinger liquid theory, are thought to describe 1D systems very well, only a few naturally occurring materials with intrinsic 1D structure are available for experimental studies. In this colloquium, I will present a new approach of synthesizing 1D quantum systems by creating dimensionally-confined stripe-superlattices from in-plane oriented 2D layered oxides. We have used this method to synthesize 1D IrO₂ stripes using a-axis oriented superlattices of Sr₂IrO₄ and insulating (La,Sr)GaO₄, both are of the K₂NiF₄ symmetry. The dimensional confinement of our 1D superlattices has been confirmed by structural characterizations. Optical spectroscopy shows clear anisotropic characteristics and one-dimensional electronic confinement of the spin-orbit split Jeff = 1/2 band. Spin and orbital excitations observed in resonant inelastic x-ray scattering spectra suggest larger exchange interactions and more confined orbital excitations in the 1D IrO₂ stripes as compared to its 2D counterpart. The observed electronic confinement and localized spin-structure are quite consistent with density functional theory calculations. This method of transforming layered materials into 1D striped structures is a viable technique for obtaining dimensional-crossover phase transitions while tuning from two- to one-dimension.

Speaker: Dr. Simien, University of Alabama at Birmingham

Abstract: Laser spectroscopy is a ubiquitous technique in modern Atomic Physics. The lineshapes obtained from atomic spectra are sensitive to important physics. For example, measuring the shape change or shift of atomic resonances is used in various settings ranging from testing the symmetry of the antiworld in antihydrogen experiments to investigating superconductivity in quantum gas systems. I will describe the application of laser spectroscopy to probe the relative nuclear charge radii of light atomic nuclei. In addition, I will describe additional experiments using precision spectroscopy in conjunction with laser cooling and trapping to investigate optical clock transitions, dipolar physics, and extremely correlated matter.

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

Abstract: Current searches for high-redshift galaxies use a combination of near-infrared filters with one or more optical filters to check for contaminants. One of these contaminants are faint dwarf stars in the disk and halo of our own Milky Way Galaxy. Thus in the search for the galaxies that caused the Reionization of the Universe, an accidental census of Dwarf stars in the Milky Way was conducted as well. I report on one observational approach with the Hubble Space Telescope; the Brightest Origin of Reionizing Galaxies (BORG) survey.

I will discuss the identification of the distant high-redshift galaxies, their unique properties, the faint brown and red dwarf stars (M-dwarfs) and our results on characterizing the shape of the Milky Way from their number. We identified stellar objects in the BoRG survey and mapped their distribution onto the Milky Way. Results are a thin disk (300pc), the rediscovery of the Sagittarius stream, a total count of 58 billion M-dwarfs in the Milky Way of which 7% reside in the halo. We also found a population of very bright, redshift eight galaxies (“Super-Eights”) that show evidence for strong nebular emission lines and direct observations of Lyman-alpha.

These M-dwarfs may be useful to register the on-sky position of NASA/ESA’s new flagship telescope, the James Webb Space Telescope and as a science byproduct of ESA’s EUCLID telescope. The Super-Eights appear to reveal a very specific mode of star-formation that may have played a critical role in the Reionization of the Universe. I will discuss future prospects.

Speaker: Renee Fatemi, University of Kentucky

Abstract: The discovery of quarks, nearly fifty years ago, launched a now classic question in particle physics: How do the interactions between quarks and gluons produce the fundamental properties of the proton? The proton electric charge is simply the sum of the valence quark charges, while the mass is largely due to the energy stored in the color fields or gluons. In contrast, it is not yet understood how the spin and orbital angular momentum of three valence quarks and a nearly infinite number of gluons and sea quarks combine to produce a spin 1/2 proton. Inclusive deep inelastic scattering experiments have limited the quark contribution to less than a third of the total proton spin. Alternative measurements and techniques, currently being pursued in experiments worldwide, are needed to provide precision insights into the gluon spin contribution and partonic orbital angular momenta. This talk will provide a historical review of spin structure experiments before discussing the most recent experimental constraints on the gluon helicity distribution (ΔG) from the spin program at the Relativistic Heavy Ion Collider.

Speaker: Duncan Farrah, Virginia Tech

Abstract: There is a deep connection between star formation and AGN activity, at all redshifts, which profoundly impacts the mass assembly history of galaxies. The nature of the connection however remains controversial, due to, for example, evolution in the AGN and starburst duty cycles, and the obscuring effect of dust. The luminous type 1 quasars are an insightful population to study in this context; accretion rates can be estimated from the UV/optical continuum shape, black hole masses can be estimated from rest-frame UV line properties, and star formation rates can be cleanly estimated from far-infrared imaging from Herschel. Our group has been studying the relationships between star formation, black hole masses and accretion rates in luminous type 1 quasars over 0.5<z<3, using data from Herschel and the SDSS. In this talk I will present some of our latest results, and discuss some implications from them for galaxy assembly at z>1.

Speaker: Dr. Guzman, University of Kentucky