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 2015 & Spring 2016 Schedule

August 7 Supermassive Black Holes and their Host Dark Matter Halos
Suchetana Chatterjee (Presidency University)

Through a plethora of observational results we now know that there is a supermassive black hole (SMBH) at the center of every galaxy in the Universe. A fraction of these harbor an active accretion disc, and are known as active galactic nuclei (AGN). Thus in the paradigm of structure formation we would like to address the question of relating SMBH to their host dark matter halos. Observationally by studying the spatial clustering of SMBH or AGN we can infer information about their dark matter hosts. AGN clustering can be characterized within a powerful theoretical framework known as the Halo Occupation Distribution (HOD). In this talk, I shall discuss HOD modeling of AGN using a fully cosmological simulation and show that the underlying theoretical model fits the two-point correlation function (2PCF) of different types of AGN. This provides us an evolutionary picture of AGN along with dark matter halos over cosmic time. In the latter half of the talk I shall provide some limitations of the 2PCF fitting method and provide alternative ways to measure the HOD of AGN while trying to address some fundamental questions in AGN physics from a cosmological point-of-view.

September 4 Mapping Galactic Dust in 3 Dimensions with Pan-STARRS1 and 2MASS
Douglas Finkbeiner (Harvard University)

2D emission-based maps have been used for decades to estimate the reddening and emission from interstellar dust, with applications from CMB foregrounds to surveys of large-scale structure. For studies within the Milky Way, however, the third dimension is required. I will present our work on a 3D dust map based on Pan-STARRS1 and 2MASS over 3/4 of the sky (, assess its significance compared to other dust maps, and say how we plan to approach the next step: R_V.

September 11 Infrared solar physics, a new era?
Philip Judge (UCAR)

I will discuss some old but fundamental problems in solar physics that can be boiled down to the deceptively simple question: "What causes the global solar magnetic field to flow and ebb, changing sign every 11 years?" I will argue that we are on the verge of some major advances using infrared technology. I will review a joint campaign to observe the infrared corona from the ground in Wyoming and from the NCAR GV aircraft during the August 21 2017 total eclipse, which passes over Wyoming. These new observations should pave the way towards a new understanding with the NSF's new flagship solar observatory, the 4 meter Daniel K. Inouye solar telescope (DKIST), scheduled for operations in 2019. These collaborations include U. Wyoming, NRL, SAO, NCAR and U. Torino. They include opportunities for undergraduate training.

September 18 New ideas in protoplanetary disk evolution
Philip Armitage (CU Boulder)

Protoplanetary disks are often assumed to evolve due to turbulent mixing of angular momentum, in the same way as accretion disks around black holes and compact objects. In the course of trying to model disk turbulence from first principles, however, we and other groups have found evidence that different processes may dominate disk evolution. Magnetized disk winds, and a form of internal magnetic braking driven by the Hall effect, may largely determine how disks evolve. I will discuss these new ideas for protoplanetary disk evolution, how they may be tested with sub-mm observations, and speculate on possible implications for planet formation.

September 25 The Puzzle of Anolamous Isotope Effect in High and Low Tc Superconductors
Prof. Guang-Lin Zhao (Southern University, Baton Rouge)

Superconductors have zero electrical resistance and expulsion of magnetic fields below a critical temperature Tc. They can carry electric current without any energy loss and have many applications. However, understanding superconductivity is a great challenge. Especially, anomalously small isotope effect in some high Tc superconductors such as YBa2Cu3O7 (YBCO) created a great challenge for understanding. TO solve the puzzle, a new methodology is implemented by integrating first-principles calculations of electronics structures of the materials into the theory of many-body physics for superconductivity. The aim is to seek a unified methodology to study the electronic and superconducting properties of the materials. It is demonstrated from first-principles that the extended saddle point singularities in the electronic structure of YBCO strongly correlate with the anomalous isotope effect in the superconductor. Some guidance for finding new high Tc superconductors will also be discussed.

October 2 Quasar Science in the Large Synoptic Survey Telescope Era
Ohad Shemmer (University of North Texas)

The Large Synoptic Survey Telescope (LSST) has been identified by the National Academy of Sciences as the highest priority ground-based observatory of the next decade. With its 8-meter aperture, LSST is designed to monitor frequently about 20,000 square degrees of the southern skies using six photometric bands for ten years. I will provide an overview of the LSST project and highlight its key science goals. In particular, I will describe how LSST will revolutionize our understanding of quasars and how such sources will be utilized as cosmological probes. I will conclude with describing the main challenges the astronomical community will face in light of the enormous data output from the telescope and the steps it is taking in preparation for LSST operations.

October 16 Thirty Meter Telescope: The Next Generation of Ground Based Optical/Infra Red Observatory
Warren Skidmore (Thirty Meter Telescope Observatory Corporation)

After a short construction status update I will discuss some of the observational capabilities that the Thirty Meter Telescope will provide and some of the areas of study that will benefit from the TMT's capabilities. I'll describe how the telescope design was developed to support a broad range of observing capabilities and how the observatory is being engineered. Finally I'll describe the avenues through which astronomers can actively participate in the project; in the planning for a potential TMT/NSF partnership, preparing for the development of 2nd generation instruments and directing the scientific aims for the observatory.

October 23 Interaction of Ferromagnetic and Superconducting Permanent Magnets - Superconducting Levitation
Ludwig Schultz, Institute of Metallic Materials, IFW Dresden and TU Dresden

Abstract TBD

November 3 Magnetic Nanowires: Revolutionizing Hard Drives, RAM, and Cancer Treatment
Beth Stadler, University of Minnesota

Abstract, TBD

November 13 INDUSTRY TALK: Translating Academic Research to a Career in Industry
Mike Borowczak (Erebus Labs)

While there is no singular path from academia to industry this talk focuses on the commonalities, differences and more importantly how to transition from the former to the latter. The discussion is grounded in the presenter's own experiences - having completed a PhD in Computer Science and Engineering and having worked in multiple roles for a Research Hospital as a Bioinformatics Programmer, two Fortune 500 Semiconductor companies as a Hardware Security Architect, and a tech startup as a Data Scientist. The objective of the presentation is to provide an overview of potential avenues and options for students looking to make a transition beyond traditional physics and astrophysics opportunities. Expect a blend of graph theory, information theory, and some straight-talk on the world outside of academia.

February 5 Workplace Ethics

Ethics in science spans a large range of topics, e.g., data honesty, authorship on papers, mentoring, sexual harrassment, etc. Recently there have been several high-profile cases of professional misbehavior in the sciences. Thus it is a good time to reflect on best practices and to discuss this important issue. We will present an overview of some statistical findings from the American Astronomy Society and then explore some interesting case scenarios. Everyone in the Department is welcome! All participants will be entered into a raffle for a $50 Amazon gift card.

February 19 From Pebbles to Planets
Katherine Kretke, Southwest Research Institute

In recent years, theories surrounding the formation of small-bodies and planets have been undergoing a radical shift. Particles with stopping times comparable to their orbital times, often called "pebbles" (although they range from sub-centimeter to meter sizes), interact with gaseous protoplanetary disks in very special ways. Gas drag can first concentrate the pebbles, allowing them to gravitationally collapse and directly produce the planetesimal building blocks, and then drag will cause them to be efficiently accreted on to these planetesimals, rapidly producing larger planetary embryos. In this talk I discuss how pebble accretion may be able to answer long standing questions in planet formation and explain the observed structure of our Solar System: by forming a system of giant planets, ice giants, and terrestrial planets; even providing an explanation for the low masses of Mars and of the Asteroid Belt.

February 23, 4:10pm in CR 215 Spin Current: The Torque Wrench of Spintronics
Mark Stiles, NIST

Spintronic devices use the spin of the electron as well as its charge. The current in these devices is spin polarized, due to the inclusion of ferromagnetic materials, so that their conductance depends on the state of the ferromagnet. This dependence allows these devices to serve as sensitive magnetic field detectors or as memory elements, in which information is stored in the magnetic state. However, not only does the polarized current depend on the magnetic configuration, but the spin current can manipulate the magnetic state. This recent development has led to rapid progress in novel memory devices. In this talk, I mention existing and proposed spintronic devices and describe the variety of ways in which the spin current can manipulate the magnetization. I focus on bilayers of ferromagnetic thin films on top of non-magnetic films with strong spin orbit coupling. Recent measurements on these systems have shown dramatic effects, but the interpretation of the experiments is still controversial, making it a fast moving exciting field.

March 25 Detection and Characterization of Exoplanetary Exospheres
Adam Jensen, University of Nebraska at Kearney

As recently as the late 1980s, the existence of planets around other stars was widely assumed by astronomers, but there was no direct observational evidence. However, much has changed in the last 20-25 years, and we are now in a golden age of exoplanet detection and characterization. I will first overview various methods of exoplanet detection and characterization, with a specific focus on the measurement of exoplanetary atmospheres. Then I will describe my research into exoplanet atmospheres, which concerns the atmospheres around hot Jupiter-class exoplanets and their extended "exospheres." The properties of exospheres have the potential to tell us about long-term atmospheric evolution, star-planet interactions, magnetic fields, and more. This work led to the first detection of excited (n=2) hydrogen in the exoplanet HD 189733b, and continues to explore this system and others for indications of exospheres and star-planet interactions.

April 1 The Miniature X-ray Solar Spectrometer CubeSat: Mission overview, spacecraft testing, instrument characterization, and solar science objectives
Christopher Moore, University of Colorado

The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is a 3U CubeSat designed to measure the solar flux from 0.5-30 keV. MinXSS student-driven involvement has been supervised by professionals with facilities support from the CU Laboratory for Atmospheric and Space Physics. MinXSS has exhibited CubeSats' capabilities as platforms for educating the next generation of scientists and engineers. In this talk, a MinXSS mission overview, satellite testing, instrument characterization, and solar science objectives will be discussed.

April 8, 4 pm in Room 195, ENZI STEM Building Emerging Functionality in Complex Oxides Driven by Sparial Confinement
E. Ward Plummer, Louisiana State University

Recent experiments clearly show that complex materials such as the transition metal compounds exhibit emergent behavior due to the strong and nonlinear coupling between charge, spin and the lattice. We also know that spatially confining materials produces new emergent phenomena (Nano-science). This talk illustrates how new behavior in Complex Transition metal oxides emerges from spatial confinement, i.e. a combination of two of themes of materials research in the 21st century: Nano and Complexity. Spatial confinement of correlated electronic systems exhibiting emergent phenomena is an indispensable step in unraveling the origin of their functionality, discovering new functionality, and opening up new applications. Materials by design (from the nano-building blocks) has been the ultimate goal of the materials community but design depends upon discover. I will also discuss the need for discovery based research in the US, and how spatial confinement can foster design driven discover and then discover driven design.

April 15 Harvesting Energy with Semiconducting Single-Walled Carbon Nanotubes
Jeffrey Blackburn, NREL

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are unique organic semiconductors with size-tunable band gaps, high absorption coefficients in the near-infrared (NIR) and visible, and extremely high charge carrier mobilities. These qualities motivate fundamental and applied studies on the use of s-SWCNTs in energy harvesting schemes, either through direct absorption in the s-SWCNTs themselves or via charge collection from organic or inorganic absorber layers. Relatively narrow bands of NIR radiation can be harvested through absorption in diameter-tunable excitonic solar cells. Alternatively, broad ranges of thermal energy (e.g. wasted heat) can be harvested in SWCNT thermoelectric (TE) materials. In this talk, I will discuss our fundamental opto-electronic studies of thin s-SWCNT films with highly tunable electronic properties. I will first discuss electrical and thermal transport in s-SWCNT films with tunable electronic structure. Fine-tuning the s-SWCNT diameter distribution and carrier density allows us to find optimal ranges for the electrical conductivity, thermopower, and thermal conductivity, enabling thermoelectric power factors that rival the highest performing polymer-based TE materials. I will then discuss time-resolved spectroscopic studies of exciton dissociation at s-SWCNT:fullerene Type II heterojunctions. We have measured ultra-fast (< 100 fs) photoninduced electron transfer across such interfaces, slow trap-mediated recombination (ns - μs), and exciton dissociation yields that are well described by the Marcus formulation for electron transfer. Finally, I will discuss the use of s-SWCNT thin films for efficient charge extraction in perovskite solar cells. The s-SWCNT charge extraction layers enable sub-picosecond removal of holes from the perovskite absorber layer, recombination times exceeding 400 μs, and improved efficiency and stability relative to traditional hole extraction layers. These studies provide insight into potential routes towards the development of efficient thin-film energy harvesting systems based on s-SWCNTs.

April 22 Electronic Structure of the Chiral Helimagnet and 3d Intercalated Transition Metal Dichalcogenide Cr1/3NbS2
Norman Mannella, University of Tennessee, Knoxville

Chiral helimagnets (CHMs) are ferromagnetic crystals belonging to chiral space groups, i.e. having a crystal structure lacking both a center of inversion as well as a mirror plane. An interesting property of CHMs is that they support extremely stable solitons, i.e. non-linear excitations that maintain their shape and energy as they propagate. A one-dimensional spin texture known as a chiral soliton lattice (CSL) has recently been observed in the CHM Chromium-intercalated Niobium Disulfide (Cr1/3NbS2[1]. The CSL function as "a tunable effective potential for itinerant electron spins, which are the current-carriers in spintronic devices. The high stability, robustness, and tunability of soliton kinks open the door to a fascinating functionality at the nanoscale" [2]. Beyond its importance in the context of CHM materials, Cr1/3NbS2 is a compelling example of a transition metal dichalcogenide (TMDC) intercalated with a 3d magnetic element (Cr). TMDCs intercalated with 3d magnetic elements with formula TxMX2 (M = Nb, Ta; X = S, Se; T = V, Cr, Mn, Fe) have been identified as ideal systems for the study of spin-textures in magnetic thin films, devices fabricated on a substrate, spin-orbit coupling effects in magnetic multilayers. Knowledge of the electronic structure of these materials is essential for the development of correct theoretical descriptions functioning as a powerful guide towards the targeted design of new CHMs and TMDCs intercalated with magnetic elements.
In this talk, I will discuss the results of our core level and angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of the chiral helimagnet Cr1/3NbS2. Intercalted Cr atoms are found to be effective in donating electrons to the NbS2 layers, but also cause significant modifications of the electronic structure of the host NbS2 material. In particular, the data provide evidence that a description of electronic structure of Cr1/3NbS2 on the basis of a simple ridig band picture is untenable. I will discuss the relevance of these results to the attainment of a correct description of the electronic structure of chiral helimagnets, magnetic thin films/multilayers, and transition metal dichalcogenides intercalated with 3d magnetic elements.
[1] Togawa et al. "Chiral Magnetic Soliton Lattice on a Chiral Helimagnet" Physical Review Letters 108, 107202 (2012).
[2] C. Pappas. "Viewpoint: New Twist in Chiral Magnetis." Physics 5, 28 (2012).

April 29 Robust and Precise Physical Measurements using Galaxy Surveys: Successes from BOSS and Lessons for the Future
Ashley Ross, The Ohio State University

Galaxy surveys allow answers to fundamental questions such as: What is the nature of Dark Energy? Can we detect deviations from General Relativity (GR)? What is the mass of the neutrino(s)? I will explain how using examples of measurements made using the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). I will describe the BOSS data, the methods we use to measure the clustering of BOSS galaxies, and how our most recent clustering measurements have allowed us to measure the distance to BOSS galaxies to within 1% precision. I will further describe some of the technical challenges and systematic concerns in our analysis, and the methods and measurements we have used to ameliorate these concerns. I will then discuss the early results from the Dark Energy Survey and the extended BOSS, both of which are in the early phases of data analysis/operation. I will conclude with a discussion of the results that will be afforded by future surveys, such as DESI.

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 2012-13 2013-14 2014-15
Contact for program information: Adam Myers