University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Prowse Room

Fall 2013 & Spring 2014 Schedule

September 13 The Golden Age of Exoplanet Discovery
Joshua Pepper (Lehigh University)

The past two decades have seen an explosion of discovery of extrasolar planets. We are now assembling a picture of the variety of planetary systems in our galaxy, detecting planets in previously unexpected configurations and types. I will describe the results from recent exoplanet surveys, including the Kepler space mission, and the ways in which our understandings of planet formation and evolution have been revolutionized. I will discuss resonant planetary systems, hot Jupiters, water worlds, iron balls, Styrofoam planets, and tatooines. I will describe the next steps in exoplanet discovery, including the work of low-cost small telescopes, and the future NASA missions that will move us toward the direct detection of biomarkers in the atmospheres of habitable exoplanets.

September 27 CANCELLED
Paul Butler (Carnegie Institute of Washington)

Modern science began with Copernicus speculating that the Earth is a planet and that all the planets orbit the Sun. Bruno followed up by speculating that the Sun is a star, that other stars have planets, and other planets are inhabited by life. For this and other heresies, Bruno was burned at the stake in a public square in Rome in 1600. Astronomy and extrasolar planets were a really hot field at the time. Over the past 20 years more than a thousand extrasolar planets have been found, first from ground-based precision Doppler and photometric transit surveys, and more recently by the Kepler space mission. We have concentrated on building precise Doppler systems to survey the nearest stars. Our systems at Lick, Keck, AAT, and Magellan have found hundreds of planets, including 5 of the first six planets, the first saturn-mass planet, the first neptune-mass planet, the first terrestrial mass planet, and the first multiple planet system. We are currently focusing our attention on new custom built "R4" echelle spectrometers designed for Iodine cells, which are yielding 1 m/s precision. These spectrometers have a footprint about the size of a ping pong table, allowing for temperature stabilization, yet deliver higher resolution and dispersion than the much larger classic echelle spectometers, such as the Lick Hamilton, the AAT UCLES, and the Keck HIRES. The two working examples, PFS on Magellan, and the Levy spectrometer on the 2.4-m APF, cost about US$2M each. They do not use fibers or scrambling, and have throughput of 20 to 30%, a factor of 2 to 4 better than classic echelles. These spectrometers will lead to the discovery of many terrestrial mass and potentially habitable planets over the next decade.

October 11
(WIRO Open House)
Title, TBA
Yiying Wu (The Ohio State University)

Abstract: A p-type dye-sensitized photoelectrode achieves charge separation through the photo-driven hole injection from sensitizers to a p-type semiconductor. It provides an attractive platform for tandem dye-sensitized solar cells and artificial photosynthesis. The challenge is in the materials design that achieves the control of directional charge transfer. In this talk, I will first present the synthesis, photophysical, electrochemical, and photovoltaic studies of a series of cyclometalated ruthenium sensitizers. I will then discuss our progresses in p-type semiconductors that require large dielectric constant, high hole mobility and properly aligned band edges. At the end, I will present an integrated electrode based on a cyclometalated ruthenium sensitizer and a cobaloxime catalyst for photoelectrochemical water reduction.

October 15 Magneto-optical Analysis of Magnetic Microstructures
Rudolf Schäfer Leibniz Institute for Solid State and Materials Research (IFW) Dresden, Germany

The rich world of magnetic microstructure or magnetic domains, extending from visible dimensions down to the nano-scale, forms the mesoscopic link between the fundamental physical properties of a magnetic material and its macroscopic properties and technical applications, which range from films for computer storage technology to magnetic cores for electrical machinery. Hysteresis phenomena, energy loss in inductive devices, noise in sensors, or the magnetoresistive properties of modern spintronic devices can be decisively determined by the peculiarities of the underlying magnetic microstructure, especially by irreversibilities in the magnetization process. Therefore any development and optimization of magnetic materials, which is usually accompanied by the measurement of magnetization curves, requires an understanding of the underlying domains and their reaction to magnetic fields, which, in most cases, can only be gained by direct imaging. In my presentation I will give a review of magnetic domains, supported by domain observation using Kerr microscopy. After a brief introduction to magnetic energies, I will demonstrate using various examples how these energies act together in the formation of domain patterns. The examples include magnetic films as well as bulk magnetic materials with different strength and symmetry of magnetic anisotropy. It will be shown how domains adapt to increasing specimen thickness (domain branching) and decreasing grain size (nanocrystalline materials and films). Most challenging is the analysis of hidden (internal) domains and processes in bulk material. They are relevant for material performance and their analysis requires surface imaging in combination with domain modeling and some volume-sensitive imaging method. Aside from their scientific and technical relevance, magnetic microstructures are also aesthetically appealing, an aspect that will be part of the presentation.

October 25 Dual Supermassive Black Holes as Tracers of Galaxy Evolution
Julia Comerford (CU Boulder)

Merger-remnant galaxies hosting dual supermassive black holes with kpc-scale separations are an expected consequence of galaxy mergers, and these dual supermassive black holes are useful as direct observational tracers of galaxy evolution. I will describe a systematic survey of dual supermassive black holes, which employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, X-ray, and radio observations to identify dual supermassive black holes that power active galactic nuclei (AGN). I will present the initial results of this search, which is building up a large observational catalog of dual supermassive black holes. This catalog will enable new observational measurements of merger-driven AGN fueling, black hole mass growth via gas accretion during mergers, and the black hole merger rate of interest for future gravitational wave experiments.

Michael E. McHenry, Carnegie Mellon University

Recent USDOE workshops highlight the need for advanced soft magnetic materials leveraged in novel designs of power electronic components and systems for power conditioning and grid integration. Similarly soft magnetic materials figure prominently in applications in electric vehicles and high torque motors. Dramatic weight and size reductions are possible in such applications. Nanocomposites also hold potential for applications in active magneocaloric cooling of such devices. Bulk and thin film soft magnet sensors can contribute to the search for oil and critical materials. Opportunities for state of the art soft magnetic materials to impact such applications have been helped by investment by USDOD Programs and other world wide efforts to advance these materials for applications in military electric vehicle technologies. This talk will focus on the framework for developing high frequency (f) magnetic materials for grid integration of renewable energy sources bridging the gap between materials development, component design, and system analysis. Examples from recent efforts to develop magnetic technology for lightweight, solid-state, medium voltage (>13 kV) energy conversion for MW-scale power applications will be illustrated. The potential for materials in other energy applications (motors, cooling, sensors, RF metal joining, etc.) will also be discussed. The scientific framework for nanocomposite magnetic materials that make high frequency components possible will be presented in terms of the materials paradigm of synthesis ā structure ā properties ā performance. In particular, novel processing and the control of phase transformations and ultimately nanostructures has relied on the ability to probe structures on a nanoscale. Examples of nanostructural control of soft magnetic properties will be illustrated.

November 8 The "Standard" Model of Cosmology ... and Open Questions
Bharat Ratra (Kansas State)

Experiments and observations over the last decade have provided strong support for a "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. I review the basic physics, astronomy, and history of ideas on which this model is based. I describe the data which persuade cosmologists that (as yet undetected) dark energy and dark matter are by far the main components of the energy budget of the universe. I conclude with a list of open cosmological questions.

November 15 Women in Physics and Astronomy Tea (NO COLLOQUIUM)
December 6 Volatile transport on Pluto and other distant icy bodies
Leslie Young (Southwest Research Institute)

Pluto and many other icy bodies are vapor-pressure equilibrium worlds, or worlds whose surface pressures are in vapor-pressure equilibrium with the dominant surface volatiles. These worlds experience an exchange of volatiles between the surface and the atmosphere, and between areas of high and low insolation on the surface. I will present a new model, called VT3D (volatile transport, 3-D), which speeds calculations by a factor of 100 or more over previous implementations. I will summarize how this new model has already opened up new investigations of Pluto and other icy Kuiper-belt objects near or beyond the orbit of Neptune, and discuss its applicability to other bodies, such as Io.

January 17 Local galaxies as laboratories to unravel the mysteries of galaxy formation and evolution
Mederic Boquien (Cambridge University)

How galaxies form and evolve across the Universe is one of the greatest outstanding questions in modern astrophysics. Yet this is a topic shrouded in mystery. To get an insight into galaxy evolution, we have to understand the fundamental process that drives the transformation of baryonic matter in galaxies: star formation. Indeed, young, blue, massive, and very luminous stars drastically affect the spectral energy distribution of galaxies, form heavy elements that enrich the interstellar medium and, due to feedback, inject metals into the intergalactic medium. Understanding how the gas reservoir of galaxies is transformed into stars is therefore pivotal to understanding galaxy formation and evolution. Unfortunately, tracing star formation and constraining star formation laws across the Universe remains a huge challenge. In this talk I will present first an overview of how to trace star formation from the ultraviolet to the far infrared, highlighting some of the recent results obtained through the study of nearby galaxies. In the second part I will explain how these nearby galaxies can be key tools to constrain models of galaxy formation and evolution, and interpret some puzzling high redshift observations.

February 7 Oxygen in the Local Universe: Error and Uncertainty in Abundances
Kevin Croxall (Ohio State University)

The metal content of a galaxy is one of the most important properties used to distinguish between viable evolutionary scenarios and strongly influences many of the physical processes in the ISM. An absolute and robust calibration of extragalactic metallicities is essential in constraining models of chemical enrichment, chemical evolution, and the cycle of baryons in the cosmos. Despite this strong dependence on abundance, the calibration of nebular abundances from nebular emission lines remains uncertain. Different calibrations of the abundance scale require different assumptions, which may or may not be valid, and measurements, not all of which are easily obtained. MODS on LBT and the late Herschel Space Observatory are allowing us to clarify this long standing calibration uncertainty. The sensitivity of MODS is enabling the detection of numerous temperature sensitive lines in nearby galaxies and Herschel observations of the [O III] 88 micron fine structure line in nearby galaxies are enabling the determination of nebular abundances that are nearly independent of temperature. I will discuss current efforts at constraining the abundance scale using these modern facilities.

February 21 Project Minerva: Small Exoplanets from Small Telescopes
Nate McCrady (University of Montana)

The Kepler mission has identified over 3000 candidate planets in the past two years, adding to the over 800 confirmed planets from radial velocity (RV) surveys. One of the most striking results of these surveys is that the number of planets increases rapidly with decreasing size. It is apparent that there are more small, rocky planets in the Galaxy than stars. These planets must be common around nearby stars, though few have yet been discovered. Finding these planets requires high precision RV measurements and high cadence observing to densely sample the orbital phase. Project Minerva is a robotic observatory dedicated to detection of rocky planets in the habitable zone around nearby stars. The observatory will consist of four 0.7-m telescopes that will use fiber optics to simultaneously feed a stable spectrograph to perform an intense campaign of precise velocimetry on the brightest, nearest, Sun-like stars. I will present simulated Minerva observations to estimate our expected exoplanet yield and habitable zone planet detections.

February 28 Synthesis and Applications of Two-Dimensional Materials beyond Graphene
Dr. Yi-Hsien Lee (Department of Materials Science and Engineering, National Tsing Hua University, Taiwan)

Recently, monolayers of transition metal dichalcogenides (TMDc), such as MoS2, and WSe2, have been reported to exhibit significant spin-valley coupling and optoelectronic performances. Monolayers in this class of materials offered a burgeoning field in fundamental physics, energy harvesting, electronics and optoelectronics. However, most studies to date are hindered by great challenges on the synthesis and transfer of high quality TMDc monolayers. Here, we demonstrate the growth of high-quality TMDc monolayers using chemical vapor deposition (CVD) with the seeding of aromatic molecules. We also present robust techniques in transferring the TMDc monolayers to diverse surfaces, which may stimulate the progress on the class materials and open a new route toward the synthesis of various novel hybrid structures.

March 6 Stars Above, Earth Below: Astronomy in the National Parks
This public presentation will be held in Room 133 of the Classroom Building at 7:30 pm.
Tyler Nordgren (University of Redlands)

Even in the 21st Century, the wide open spaces of the American West allow us to set out on many a trail or dirt road and imagine we are one of the region's early explorers. Yet when the sun goes down, that illusion is shattered in all too many places. Increased urban lighting is now so bright and widespread that fewer than 60% of Americans and Europeans can even faintly glimpse the Milky Way at night from their homes. For most Americans, the national parks that have preserved the landscape for the last one hundred years have also preserved the views of dark starry skies overhead. Today a naturally starry sky is as rare as the grizzly bears, glaciers, and granite gorges that bring visitors to the parks. A new grassroots initiative within the parks is looking to bring the beauty of the West to visitors from around the world: a beauty on display by day as well as by night.

March 7 Ground-based observations of Io's volcanoes in support of spacecraft missions
This colloquium is supported by EPSCoR's Wyoming Women in Science and Engineering (WWISE) program and by NSF Grant #1208909
Julie Rathbun (University of Redlands)

As spacecraft move out further into the solar system, astronomers have been pushed aside in favor of planetary geologists. However, ground-based telescopes still have much to tell us about our own solar system, especially when combined with spacecraft data. Jupiter's moon Io is the most volcanically active object in our solar system. It has been studied by the Voyager, Galileo, and New Horizons spacecrafts. However, the high activity leads to a constantly changing environment and snapshots from spacecraft are unable to tell us how the volcanic activity changes. Here I will present ground-based observations from NASA's Infrared Telescope Facility (IRTF) that were taken to complement spacecraft data. These data tell us which volcanoes are active and how active they are, as a function of time. This activity constrains models of how the volcanoes erupt, and have demonstrated that Loki, the largest and most powerful volcano on Io is likely an overturning lava lake.

March 12 Tripping the Light Nano-tastic: Trends Toward Integrated Photonics
Joshua Bodyfelt (Massey University, New Zealand)

In commercial state of the art computing there is a current trend toward photonics (including obstacles). Motivated by this, three projects will be presented. The first discusses filtering in photonic structures using thin magneto-metallic films. The second introduces parity-time symmetry (PT) which shows rectification in a nonlinear dimer setup, as experimentally realized by standard benchtop electronics. The last project reviews the nonlinear dynamics of noisy, yet tunable, photonic oscillators. The talk concludes with a conjecture along these research directions.

April 2 (Wednesday) Women in Physics & Astronomy Tea

April 4 Dusty Galaxies, Blurry Backgrounds, and how I learned to stop worrying about and love statistical methods
Marco Viero (Caltech)

Far-infrared/Submillimeter wavelengths provide a unique window into obscured star formation at high redshifts, with the full ensemble of dusty star-forming galaxies combining to make up the Cosmic Infrared Background (CIB). However, source confusion - a noise floor which is present in maps where the PSF is large enough to contain multiple sources - makes identifying individual sources and relating them to their optical counterparts incredibly challenging. Given these limitations, I will outline (relatively simple) techniques designed to statistically make this connection, and I will present latest results from HerMES on the evolving physical properties of these infrared galaxies, including their redshift distributions, clustering properties, temperatures, and luminosity densities. I will show how these properties are intimately tied to their host galaxy stellar mass and redshift, and then summarize their implications for galaxy evolution and cosmology. I will finish by presenting HeLMS and HerS, two new Hershel surveys in the Stripe 82 which were designed to leverage the rich set of ancillary data in the stripe to better answer these and other exciting questions.

April 11 Multivalent Dendrimer Nanoplatform for Targeting Bacterial Surface
Dr. Seok Ki Choi (Department of Internal Medicine, Michigan Nanotechnology Institute for Medicine and Biological Studies, University of Michigan Medical School)

This talk will discuss the use of multivalent design as an effective strategy for designing bacteria-targeting nano delivery systems. We designed a series of fifth generation poly(amidoamine) dendrimers tethered with a bacteria-targeting ligand at different valencies. Vancomycin and polymyxin B were employed as the preferred ligand for targeting Gram(+) and Gram(-) bacteria, respectively. We performed surface plasmon resonance studies to determine their binding avidity to two types of cell wall models, each made with either D-Ala-D-Ala (or D-Ala-D-Lac) peptide for Gram(+) cell wall or lipopolysaccharide for Gram(-) cell wall. Each of these conjugates showed remarkable enhancement in avidity in the targeted cell wall model with at least four orders of magnitude greater than the free ligand. Such tight adsorption of the conjugate to the model surface corresponded with its ability to bind bacterial cells as illustrated by detection of Staphylococcus aureus bacterial cells bound in vitro by confocal fluorescent microscopy. The bacteria-targeting dendrimer platform was then used to fabricate the surface of iron oxide nanoparticles by coating them with the dendrimer conjugates, and the resulting dendrimer-covered magnetic nanoparticles were demonstrated to rapidly sequester bacterial cells. In summary, this talk will describe the design and biophysical basis of the tight, multivalent association of dendrimer conjugates to the bacterial cell wall, and proposes potential new uses of this nanoplatform for antibacterial applications.

April 25 Harnessing Defects in Graphene: from Plasmonics to Chemical Functionalization
Dr. Kirill Velizhanin (Theoretical Division, Los Alamos National Laboratory)

Graphene - a truly two-dimensional one-atom thick sheet of carbon - is a promising new material with potential applications ranging from photovoltaics to nanoelectronics and photonics. Specifically, with carrier mobilities reaching up to ~106 cm2/Vs graphene is expected to become a major player in nanoelectronics serving as a high-quality thin flexible conductor. Obviously, for such applications the concentration of carrier-scattering defects has to be minimized to improve the performance of a graphene-based device. However, there is a multitude of applications where defects in fact can be beneficial as they can tailor the electronic, transport, optical and mechanical properties of graphene. Since graphene is an "all-surface" material, the effect of this tailoring on properties of graphene could be very strong, resulting in essentially new materials. An important example is a controlled chemical functionalization of graphene (graphane, halogenated graphene, graphene oxide) with the goal to tailor its electronic band structure. In my talk, I will report on our recent progress in studying the effect of various "defects" (semiconductor quantum dots, chemical groups) on electronic, optical and thermodynamic properties of graphene. Specifically, I will talk about an emerging field of graphene plasmonics and (non-) equilibrium thermodynamics of chemically functionalized graphene.

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006 Spring 2007 Fall 2007 Spring 2008 2008-09 2009-10 2010-11 2011-12
Contact for program information: Adam Myers