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Events: Departmental Colloquia

  • Probing the Beginnings of Planetary Birth in the Age of ALMA

    Guest: Edwin Bergin, Professor and Chair of Astronomy, University of Michigan
    Thursday, March 3, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The Atacama Large Millimeter Array (ALMA) has begun operations in the high desert of northern Chile offering unprecedented spatial resolution and sensitivity within the millimeter and sub-millimeter atmospheric windows. The study of planet birth is one of the key science areas enabled by ALMA due to the ability to resolve both gas and dust emission within the planet formation zones of young gas-rich circumstellar disks. This is highlighted by the fantastic high resolution image of HL Tau showing significant structure in the emission from pebbles within a young disk that is still accreting from its natal envelope. In this talk I will explore the related physics and chemistry of gas-rich disks and emphasize new breakthroughs in our understanding brought about by ALMA in concert with data from the Herschel Space Observatory. In particular I will report on the physical/chemical links in terms of snow-lines and the likely formation of pebbles and possibly planetesimals. Snow-lines represent chemical transitions (ice to vapor) in the disk and have long been posited as favorable sites for planet formation. With ALMA we have now directly and indirectly resolved the carbon monoxide snow-line in several disk systems. I will present these data and show compelling new evidence that grain growth is fostered at these locations, perhaps giving rise to the fantastic structure seen in HL Tau. Furthermore the formation of ice-coated pebbles in the increasingly dust rich midplane must deplete the upper layers, and due to radial drift, the outer disk of key ices that carry C, H, O, N. We will show that there is strong evidence for missing volatiles in the disk surfaces layers of the nearest disk system (TW Hya) with an apparent radial gradient in the carbon to oxygen content in the gas and solids. This elemental abundance gradient will likely be imprinted within the atmospheres of forming gas giants and sets constraints on the location of the volatile reservoir needed to form habitable terrestrial worlds.
  • Nanotechnology Innovations at SRNL: Fundamentals and Applications

    Guest: Simona E. Hunyadi Murph, Savannah River National Laboratory
    Thursday, February 11, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Even though Nature provides us with an outstanding selection of materials that can improve our lives, their range and abundance is still surprisingly lacking in the contemporary world. The possibility of finding new and intriguing materials that can cure disease, help us explore and/or live in space, make us live longer and healthier lives, increase communications between people around the world, and discover new energy supplies is exhilarating. The promise of viable applications for the future lies in the ability of scientists to understand, generate and control materials at the nanoscale. The development of multifunctional nanomaterials opens up new avenues for the creation of multi-purpose technologies that can be used for numerous applications. Multifunctional nanoparticles take advantage of the physicochemical properties of two or more materials. This creates a new multifunctional composite nanostructure with tailored optical, surface, and structural properties which serve as a multimodal probing agent. Metallic nanoparticles (Au, Ag, Pt, Pd), metallic oxide nanoparticles (TiO2, Fe2O3, SiO2) or a combination of these will be the main focus of this presentation. Specifically, I will discuss our recent synthesis and characterization techniques used to create different size, shape, composition, and morphology of multifunctional nanostructures. Representative applications pertinent to chemical sensing, imaging, and environmental cleaning, etc. of these advanced nanostructures will be described.
  • Hamilton-Jacobi Trajectories of Comets Kohoutek and ISON: A Novel Approach to Celestial Dynamics

    Guest: Prof. M. Howard Lee, UGA Physics And Astronomy
    Thursday, January 28, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (Room 202)

    There is a class of comets which visit the solar system once and never return. These events are rare, occurring but once or twice a century. Kohoutek observed in 1973 and ISON in 2012 belong to this class. These remarkable comets are physically characterized by the eccentricity e very nearly 1. Thus their trajectories would seem of special interest to celestial dynamics. By Hamilton-Jacobi theory we have obtained a general solution for the trajectory in a two-body solar system. If e<1, the solution contains Kepler's three laws. If e>1, it yields an analog of Kepler's law 2, not previously known perhaps. The trajectories for the two special comets are obtained by taking the e-->1 limit on the general solution. By a "horizon singularity" one can determine how they disappear from the solar system. By this singularity one can identify this class of comets as they approach the solar system.
  • Rethinking Introductory Physics for Life Science Students: A Model for Deep Curriculum Reform

    Guest: Edward Redish, Department of Physics, University of Maryland
    Thursday, January 21, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (Room 202)

    For the past five years, a multi-university interdisciplinary team led by the University of Maryland's Physics Education Research Group has been rethinking the role that a physics class can play for biology majors and pre-meds. We found some surprising results. Some of the things we had been doing turned out to be of little value for this population; and we learned there were valuable things we could do for them that hadn't even occurred to us to try. I'll review some of our decisions and what we have learned. I'll spend the last few minutes of the talk speculating on some of the questions an approach like this raises for the physics curriculum for majors and engineers.

    References:
    Reinventing physics for life science majors, D. C. Meredith and E. F. Redish, Physics Today, 66:7 (2013) 38-43.
    Toward better physics labs for future biologists, K. Moore, J. Giannini, & W. Losert, Am. J. Phys., 82:5 (May, 2014) 387-393.
    Chemical energy in an introductory physics course for the life sciences, B. W. Dreyfus, B. D. Geller, J. Gouvea, V. Sawtelle, C. Turpen, & E. F. Redish, Am. J. Phys., 82:5 (2014) 403-411.

  • The Quenching of CO: The Complex Story of an Almost Homonuclear Molecule

    Guest: Professor Phillip Stancil, UGA Physics and Astronomy
    Thursday, November 19, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Carbon monoxide (CO) is detected in nearly every astronomical source from comets to high redshift quasars. It is observed in absorption in the UV, and by emission due to rotational and vibrational transitions from the near IR to submillimeter wavelengths. In most environments, CO rovibrational levels have populations far from thermal equilibrium so that the populations are determined primarily by collisions with dominant neutral species (H2, He, H). While collisional excitation of CO has been studied theoretically and experimentally for many decades, it may seem surprising that large uncertainties, orders of magnitude in some cases, remained in our knowledge of key parameters until now. It is only in recent years that computational resources and algorithms have advanced sufficiently that nearly exact, full-dimensional calculations have become feasible. In this talk I will highlight our recent computational work on full-dimensional scattering calculations, focusing on the CO-H, CO-H2, and CO-He collision complexes for rotational and vibrational excitation. I will also discuss the role of collisional data in astrophysical modeling.
  • Functional Oxide Materials Discovery by Epitaxial Design

    Guest: Dr. Ho Nyung Lee, Oak Ridge National Laboratory
    Thursday, October 15, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Complex oxides are known to possess the full spectrum of fascinating properties, including magnetism, colossal magneto-resistance, superconductivity, ferroelectricity, pyroelectricity, piezoelectricity, multiferroicity, ionic conductivity, and more. This breadth of remarkable properties is the consequence of strong coupling between charge, spin, orbital, and lattice symmetry. Spurred by recent advances in the synthesis of such artificial materials at the atomic scale, the physics of oxide heterostructures containing atomically smooth layers of such correlated electron materials with abrupt interfaces is a rapidly growing area. Thus, we have established a growth technique to control complex oxides at the level of unit cell thickness by pulsed laser epitaxy. The atomic-scale growth control enables to assemble the building blocks to a functional system in a programmable manner, yielding many intriguing physical properties that cannot be found in bulk counterparts. In this talk, examples of artificially designed, functional oxide heterostructures will be presented, highlighting the importance of heterostructuring, interfacing, and straining.

    The main topics include (1) fast, reversible redox reactions in epitaxial 'SrCoOx oxygen sponges' and their strain control for improved catalytic oxygen reduction reaction, (2) understanding oxygen vacancy stability in layered oxides: brownmillerite and Ruddlesden-Popper oxides, (3) orbital polarization in LaNiO3 thin films for improved oxygen catalysis, (4) improving carrier transport and thermoelectric power of oxide 2D electron gases in LaTiO3/SrTiO3 superlattices by fractional delta doping, and (5) spin-orbit coupling in SrIrO3 thin films and heterostructures.

  • Calories for Quarks: The Origin of Visible Mass in this Universe

    Guest: Craig Roberts, Argonne National Laboratory
    Thursday, October 1, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The 2013 Nobel Prize in Physics was awarded to Higgs and Englert following discovery of the Higgs boson at the Large Hadron Collider. With this discovery the Standard Model of Particle Physics became complete. Its formulation and verification are a remarkable story. However, the most important chapter is the least understood. Quantum Chromodynamics (QCD) is that part of the Standard Model which is supposed to describe all of nuclear physics and yet, almost fifty years after the discovery of quarks, we are only just beginning to understand how QCD builds the basic bricks for nuclei: pions, neutrons, protons. Critically, the Higgs boson is often said to give mass to everything. However, that is wrong. It only gives mass to some very simple particles, accounting for only one or two percent of the mass of more complex objects. The vast majority of mass comes from the energy needed to hold quarks together inside nuclei. I will explain this remarkable emergent phenomenon, contained fundamentally in Nambu's share of the 2008 Nobel Prize, and discuss its connection with the peculiar feature of confinement in QCD, /viz/. the fact that quarks are forever imprisoned, never reaching the freedom of a particle detector; and show how contemporary and future terrestrial experiments can help complete the book on the Standard Model.
  • Changing Undergraduate STEM Instruction: Supporting the Learning and Instruction of Faculty

    Guest: Kenneth A. Johns, Department of Physics, University of Arizona
    Thursday, September 17, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    There is general acceptance among administrators and faculty that undergraduate STEM instruction needs to change. However, this is much easier for faculty and administrators to discuss than implement in universities that have a research mission. In this talk, I will share how STEM faculty at the University of Arizona became involved in a project that focused on improving undergraduate STEM instruction. Specifically, through different project initiatives there is support for the transformation of STEM faculty instruction and of department cultures to sustain the use of evidence-based, active learning instruction.
  • Inside-Out Planet Formation

    Guest: Prof. Jonathan Tan, Department of Astronomy & Physics, University of Florida
    Thursday, August 27, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The Kepler-discovered systems with tightly-packed inner planets (STIPs), typically with several planets of Earth to super-Earth masses on well-aligned, sub-AU orbits may host the most common type of planets in the Galaxy. They pose a great challenge for planet formation theories, which fall into two broad classes: (1) formation further out followed by migration; (2) formation in situ from a disk of gas and planetesimals. I review the pros and cons of these classes, before focusing on a new theory of sequential in situ formation from the inside-out via creation of successive gravitationally unstable rings fed from a continuous stream of small (~cm-m size) "pebbles," drifting inward via gas drag. Pebbles first collect at the pressure trap associated with the transition from a magnetorotational instability (MRI)-inactive ("dead zone") region to an inner MRI-active zone. A pebble ring builds up until it either becomes gravitationally unstable to form an Earth to super-Earth-mass planet directly or induces gradual planet formation via core accretion. The planet continues to accrete until it becomes massive enough to isolate itself from the accretion flow via gap opening. The process repeats with a new pebble ring gathering at the new pressure maximum associated with the retreating dead-zone boundary. I discuss the theory’s predictions for planetary masses, relative mass scalings with orbital radius, and minimum orbital separations, and their comparison with observed systems. Finally I speculate about potential causes of diversity of planetary system architectures, i.e. STIPs versus Solar System analogs.
  • The Broken Geometry of Life

    Guest: Prof. Michael Bachmann, Department of Physics and Astronomy, The University of Georgia
    Thursday, August 20, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Biomolecules such as proteins are finite and small (but not microscopic) systems that are of "in-between"sizes, i.e., they exist on mesoscopic length scales. This means, they are too large to allow for a quantum-chemical description of their physical properties and too small for a classical macroscopic approach. They do not even exhibit long-range symmetries, which would be helpful for their theoretical modeling. Nonetheless, processes that lead to functional structures of such molecules in a complex thermal environment surprisingly exhibit features known from thermodynamic phase transitions. Since the thermodynamic limit is out of sight, sophisticated computer simulations are currently the only way for the systematic study of the statistical mechanics of structural transitions in these systems. The striking finite-size effects that influence or even govern processes on mesoscopic scales lead to a couple of fundamental questions such as: What is temperature? In this talk, revised statistical mechanics concepts for finite systems, molecular models, and simulation methods are introduced. Examples of generic molecular structure formation processes such as protein folding, polymer aggregation, and macromolecular adsorption on solids will be discussed.
  • Violent Events in Rocky Planetary Systems

    Guest: Ben Zuckerman, Research Professor and Emeritus, UCLA
    Thursday, March 5, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Implications for the fate of technological civilizations, including our own

  • Computer Simulation Studies of Polymer Adsorption and Aggregation - From Flexible to Stiff

    Guest: Prof. Wolfhard Janke, University of Leipzig
    Thursday, February 26, 2015 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    An overview is given on recent computer simulation studies of polymer adsorption and aggregation using generic coarse-grained models. The simulations are performed with Monte Carlo methods in generalized ensembles (multicanonical and parallel tempering) and analyzed from a canonical and microcanonical view. As examples polymer chains interacting with a flat patterned surface or being confined in a spherical cage will be discussed. Of particular interest is the scaling behavior of conformational transitions in dependence of the polymer's bending stiffness. Bending stiffness also  plays a key role for semiflexible polymer aggregation. Our results show that this is the distinguishing parameter that controls whether amorphous aggregates or twisted bundle-like motifs are formed.

  • Research on Transfer and Implications for Learning and Problem Solving

    Guest: Dr. Sanjay Rebello, Kansas State University
    Thursday, January 22, 2015 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Transfer of learning is often described as the overaching goal of education.  I will provide a broad overview how the theoretical perspectives on transfer of learning have evolved over time and delve deeper one perspective of transfer that has served as an overaching framework for some of the projects in our reasearch group over the past few years.  In particular I will discuss projects that utilize this perspective to facilitate problem solving. One of these projects focuses on facilitating transfer of mathematical integration to problem solving in a calculus-based physics course for future engineers. The other focuses on the use of visual cueing to facilitate learning and problem solving. I will discuss how these interdisciplinary efforts have advanced our knowledge of how students learn and solve problems in STEM disciplines.

  • Are the Parameters of the Standard Model fine-tuned for Carbon-based Life?

    Guest: Prof. Dean Lee, NC State
    Thursday, December 4, 2014 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    I discuss some recent results obtained using ab initio lattice simulations of effective field theory to probe nuclear structure. I present recent lattice calculations of the Hoyle state of 12C and whether or not light quark masses must be fine-tuned for the viability of carbon-based life.

  • Exoplanets Exposed: The current revolution in directly imaging exoplanetary systems

    Guest: Paul Kalas, UC Berkeley
    Thursday, November 20, 2014 1:30 pm - 2:30 pm
    Location: Physics Auditorium (202)

    There are now several thousand planets known outside of our solar system, but most have been discovered by indirect means. Directly imaging exoplanets is an enormous challenge, sometimes compared to detecting a firefly next to a lighthouse. The last time a newplanet had been discovered through astronomical imaging was our own Neptune in 1846. Within the last ten years, however, advances in space and ground-based instrumentation have provided a handful of new exoplanets discovered by direct imaging. Here I will review the techniques that are used and the Hubble Space Telescope discovery of an exotic planet called Fomalhaut b. Among the directly imaged exoplanets,Fomalhaut b has unexpected characteristics, such as a relatively blue spectrum and a highly eccentric orbit, leading to hypotheses that it is a gravitationally scattered, low-mass planet hosting a giant planetary dust ring or cloud seen in reflected light. Also in 2013-2014, the Gemini Planet Imager (GPI) was successfully commissioned. I will review our accomplishments with GPI so far and discuss our research plan that over the next three years will provide an atlas of 25-50 new exoplanets orbiting nearby stars.

  • Conquering NMR sensitivity Limitations: DNP Enhanced studies of Cellular Metabolism

    Guest: Dr. J. H. Prestegard, UGA CCRC
    Thursday, November 13, 2014 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Nuclear Magnetic Resonance (NMR) has found applications in fields running from physics, to chemistry, to structural biology and medicine. In all cases sensitivity has been a limitation, requiringmilligramquantitiesofsampleorexceedinglongsignalaveragingperiods. The latter can be particularly limiting for real-time metabolism studies where transit between substrate and product can occur on a time-scale of tens of seconds. Recently Dynamic Nuclear Polarization (DNP) has reemerged as a means of improving NMR sensitivity by many orders of magnitude. DNP enhanced in vivo monitoring of metabolism for cancer diagnosis is near the point of clinical application. Emphasis has been on the conversion one substrate (pyruvate) to a product (lactate). However, the potential for developing substrates that probe other metabolic pathways and elucidate mechanisms of participating enzymesisenormous. This presentation will cover some of the basic physics underlying DNP and illustrate applications with results from enzyme mechanism and in-cell studies on-going at UGA.

  • LSST and Dark Energy

    Guest: Elliott Cheu, University of Arizona
    Wednesday, November 5, 2014 4:30 pm - 5:30 pm
    Location: Physics Auditorium (202)

    I will discuss the current understanding of dark energy and dark matter. Current and future astrophysical surveys should shed light on the amazing fact that the expansion of our Universe has accelerated in recent time. The upcoming Large Synoptic Survey Telescope should provide the most comprehensive dataset available to help answer the question about the nature of dark energy.

  • Defining Chaos from First Principles

    Guest: M. Howard Lee, UGA Physics and Astronomy
    Thursday, October 23, 2014 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

  • Magnetic Resonance Imaging with Hyperpolarized <sup>13</sup>C

    Guest: Dr. Jeremy Gordon, Department of Radiology and Biomedical Imaging University of California San Francisco
    Thursday, April 24, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    Magnetic resonance imaging (MRI) of 13C nuclei holds the potential to probe pathology at a molecular level. These pathological changes often times precede or occur in the absence of changes in anatomy and can therefore provide valuable insight into the treatment of malignant diseases. Unfortunately, signal from endogenous 13C is indistinguishable from noise due to low receptivity, sub millimolar in-vivo concentrations, and scan time limitations.

    Recent advances now allow for >10,000 fold signal enhancement of 13C nuclei via a technique referred to as dynamic nuclear polarization (DNP), enabling the use of 13C labeled molecules to probe metabolic function non- invasively and in real-time. Nevertheless, MR imaging of hyperpolarized 13C compounds is more challenging than conventional 1H MRI, due in large part to the nature of the hyperpolarized magnetization and the need to generate images of both the substrate and the metabolic products. In this talk we will discuss the principles of hyperpolarization, the basics of MRI with hyperpolarized 13C compounds, and some of the applications of this new and exciting technique.

  • Second chance planets

    Guest: Prof. Alex Wolszczan, Penn State University, Department of Astronomy & Astrophysics Center for Exoplanets and Habitable Worlds
    Thursday, April 10, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    New planets can be created in collisions following the dynamical evolution of original planetary systems circling evolving giant stars. They can also arise from supernova fallback disks around newborn neutron stars and debris disks surrounding white dwarfs. These seemingly far-fetched ideas have been confirmed through discoveries of planets around pulsars, sub-dwarfs, and, possibly, around white dwarf stars, all of which demonstrates the spectacular robustness of the planet formation process. Furthermore, life itself may get a new chance, when habitable zones around evolving giants encompass faraway worlds like Europa and Titan in the solar system. In this talk, I will review the development of this particular field in the exoplanet research and present the Penn State-Torun Centre for Astronomy search for planets around GK-giants with the 9.2-m Hobby-Eberly Telescope.

  • Star Formation in Ultraluminous and Infrared Bright Galaxies

    Guest: Dr Sarah Higdon, Department of Physics, Georgia Southern University
    Thursday, April 3, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium Rm. 202

    How stars and galaxies form and evolve is one of the fundamental questions in the field of astrophysics. Star formation in the early Universe occurred at a higher rate than the present day and often in extremely dusty environments. The brightest galaxies are known as ultraluminous galaxies and are the product of galaxy mergers. These galaxies are hidden to optical telescopes and require observations in the infrared/sub-millimeter range.  ZEUS-2 is the second generation Redshift (Z) and Early Universe Spectrometer (P.I. Gordon Stacey, Cornell University).  It is designed to study star formation in galaxies from their birth in the early Universe around 12-billion years ago, through to the present day. In the “local” universe (z < 0.1) ZEUS-2 targets the warm molecular gas cooling lines of 12CO(J=8-7, 7-6, and 6-5), and 13CO(6-5) and the neutral atomic carbon lines  [CI] 370 micron and 610 micron. In the early universe (z>1) the telluric windows correspond to the redshifted fine structure lines of [CII] 158 micron, [OIII] 88 micron, [OI] 63 micron, and [NII] 122 micron and 205 micron. I will demonstrate how far-infrared and submillimetre observations can be used to investigate the physical properties of the interstellar medium in a sample of galaxies. In the process I will highlight some of the results from the ZEUS-2 consortium.

  • Towards accurate quantum dynamics of macromolecular systems on classical and quantum computers

    Guest: Prof. Phillip Stancil, Department of Physics and Astronomy, University of Georgia
    Thursday, March 27, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    While the past decade has seen tremendous advances in (classical) computing technologies (CPUs, GPUs, accelerators), in methodologies for molecular electronic structure, and in accurate representation of high-dimensional molecular potential energy surfaces, comparable advances in quantum dynamics computation have generally lagged. Likewise, advances in quantum computing hardware have motivated development of quantum simulation algorithms for molecular structure problems, but less so for dynamics applications. In the first half of this talk, I'll review the current status of inelastic and reactive scattering calculations for high-dimensional molecular systems on classical computers focusing on methods and size limitations for practical calculations. In the second half, the single excitation subspace (SES) approach to quantum simulation will be introduced as applied to the time-dependent Schroedinger equation [1,2]. Demonstrations of the method will be given for simulations of simple atom-atom collision systems as envisioned on large networks of coupled superconducting quantum computing devices. Resource estimation comparisons between classical computations and SES simulations will be addressed as well as the prospects for performing quantum simulations of macromolecular systems, highlighting the largest systems computable today on classical devices.

  • Photophysical properties and applications of CdSe quantum dots.

    Guest: Prof. Ho-Soon Yang, Department of Physics, Pusan National University, Busan, Korea
    Thursday, March 20, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    Colloidal semiconductor nanocrystals have been of interest in aspects of fundamental understandings and applications such as light emitting diodes, lasers, photovoltaic cells, biomedical tags and solar cells. The optical and electronic properties of CdSe quantum dots (QDs) show a strong size and shape dependence. QDs have a high ratio of surface to volume and the surface of QDs prepared with a chemical method has a complex condition due to organic ligands. Therefore, the complex surface condition of colloidal QDs plays an important role in determining quantum yield (QY), carrier relaxation, and recombination process. The asymmetric crystal field and electron-hole exchange interaction in CdSe splits the lowest exciton state, (1se-1sh2/3), into five levels which includes the ‘dark’ and ‘bright’ exciton states. CdSe QDs are synthesized in wurtzite structure using the chemical colloidal method in this study. The optical modal gain enhancement of CdSe QDs is observed in a cylindrical glass-waveguide by using a variable stripe length method. CdSe QDs are prepared as having various surface conditions, which induces QY to be changed. The time resolved spectra show two different energy relaxation processes, a fast process of electron hole combination and a slow process involved with surface states. The ratio of slow to fast processes increases as the QY increases, which reveals that the surface related emission contributes to high QY of QDs. The photoluminescence and time resolved spectra are obtained over a broad temperature range (4 ~ 300K). The dark and bright exciton states are observed at a low temperature regime.

  • Spin-polarized organic light emitting diode based on a novel bipolar spin-valve

    Guest: Prof. Tho Nguyen, UGA Physics and Astronomy
    Thursday, March 6, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    The spin-polarized organic light emitting diode (spin-OLED) has been long sought device within the field of Organic Spintronics. We designed, fabricated and studied a spin-OLED with ferromagnetic (FM) electrodes that acts as a bipolar organic spin valve (OSV), based on deuterated derivative of poly(phenylene-vinylene) with small hyperfine interaction [1]. In the double-injection limit the device shows ~1% spin-valve magneto-electroluminescence (MEL) response that follows the FM electrode coercive fields, which originates from the bipolar spin-polarized space charge limited current [2]. Our findings provide a pathway for organic displays controlled by external magnetic fields. Here is the outline of my talk. First, the background of magneto-resistance in OLEDs and OSVs are reviewed. Next, I present some previous attempts to achieve spin-OLEDs. Finally, I show our success on demonstrating spin-LEDs. If the time permits, I will go over the current advances toward Organic Spintronics in our laboratory.

  • Emergent phenomena via molecular dynamics

    Guest: Prof. Dennis Rapaport, Bar-Ilan University, Israel
    Thursday, February 27, 2014 4:00 pm - 5:00 pm
    Location: Physics Auditorium (202)

    Emergent phenomena share the fascinating property that they are not obvious consequences of the design of the system in which they appear, a characteristic equally relevant when attempting to model them. We describe several systems that exhibit surprisingly rich emergent behavior, each studied by molecular dynamics (MD) simulation. Modelling self-assembly processes relevant to virus growth reveals the ability to achieve complete, error-free assembly, where, paradoxically, high yields are due to reversible bond formation. In the case of fluids studied at the atomistic level, not only can complex hydrodynamic phenomena in rotating and convecting fluids -the Taylor-Couette and Rayleigh- Benard instabilities - be reproduced within the limited length and time scales accessible to MD, but there is even quantitative agreement. Finally, studies of granular mixtures show behavior that, in the case of a rotating drum, reproduces the familiar counterintuitive axial and radial segregation, and in the case of a vertically vibrated layer, indicates a novel form of horizontal segregation. While there are limitations to the MD approach, both conceptual and computational, the present results offer a tantalizing hint of what can be accomplished.

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