Physics Colloquium

Fall 2010

Thursdays 4:00 p.m., Room 104 Physics
Refreshments served at 3:40 p.m.
  Colloquium organizer: Alexey Yamilov
(Link to main colloquium page)

Green - open date
Yellow - tentative (reserved)
Red - firm commitment

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Date Host Speaker Title of the talk Abstract
Sept. 2 Olson David Crandall
National Nuclear Security Administration
Progress at the National Ignition Facility:
Prospects for Science and Energy through Inertial Confinement Fusion

Lecture recording:
Streaming Link
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Beginning in the 1960’s, a concept called inertial confinement fusion (ICF) has evolved for rapid compression of a small capsule of deuterium and tritium, creating a miniature nuclear explosion in the laboratory as a method of controlled release of fusion nuclear energy.  The required physical conditions are both extreme and delicate and have been studied, attempted and simulated for 50 years.  The concept came from nuclear weapon designers who want to tame nuclear explosions, conducting them repeatedly in a laboratory environment.  Expectation is high that the first such laboratory, pure fusion ignition event (more fusion energy out of the target than compression energy into it) may be achieved within a year at the $3.5 B, 192-laser-beam National Ignition Facility (NIF) at Livermore, CA.  The physical conditions for “hot spot” ignition inside the “hohlraum” of a fusion target driven “indirectly” by the megajoule laser system will be described in this talk.  Called both “a star in the laboratory” and “the internal combustion engine of the 21st century”, the advent of ignition opens ways to do science and provide industrial energy that are new.  Potential for adapting this new capability to astrophysical experiments and commercial fusion energy will be described.
Sept. 9 Jentschura     Jonathan Sapirstein
Notre Dame
What is the size of the proton? One application of precision atomic theory is the determination of nuclear properties. In recent years hydrogen spectroscopy has allowed a determination of the size of the proton more accurate than that available from electron scattering experiments. In this talk this situation is reviewed, and surprising new results in apparent conflict with the results from hydrogen coming from muonic hydrogen are discussed.
Sept. 16 Dubois Bob Dubois
Missouri S&T
Scientific and Personal Benefits and Experiences Associated with a Sabbatical Leave This talk will detail my experiences, both scientific and personal, during my recent sabbatical to Germany where I was a Fulbright Fellow at the Ruprecht-Karls-Universität Heidelberg and a guest professor at the ExtreMe Matter Institute at the GSI Helmholzzentrum für Schwerionforschung in Darmstadt.  Part of the talk will consist of an overview of the research I was involved in plus that being done at various labs I had a chance to visit, both within and outside Germany.  The other part of the talk will consist of personal experiences associated with living, working, and traveling abroad.
Sept. 23 Medvedeva Haeyeon Yang
Utah State University
Guided assembly of nanodots through selective heating Difficulties in control of the size and position of self-assembled nanostructures have been regarded as major obstacles to bringing their full potentials into commercialization, such as high efficiency solar cells. Many approaches were tried to control placements of nano dots, which includes nano patterning to take advantage of different diffusion kinetics depending on facet orientations, nano patterning then growth of stressor layers, and use of  high index surfaces.
   Interferential irradiation is a relatively simple process to control the placement and can be applied to any substrates and coupled with various growth techniques. Interferential irradiation of high power laser pulses has been used to create and align self-assembled metallic nano dots on glass substrates. Self-assembled nano dots by applying interferential irradiations of high power laser pulses on semiconductor surfaces have not been reported yet.
   In this talk, guided assembly of nanodots on InGaAs epilayers on GaAs(001) substrate will be discussed. Spatial thermal modulations in nanoscale were created in-situ on the epitaxial growth fronts in the Molecular Beam Epitaxy (MBE) growth chamber by employing interferential irradiations of high power laser pulses. As-irradiated surfaces were examined using the attached ultra-high vacuum Scanning Tunneling Microscope (STM). STM images indicate that self-assembled dots are formed due to the irradiation. Furthermore, the dot density modulates sinusoidally with a periodicity similar to that of the interference. The morphological analysis of dots and the implications on the growth mechanism will be discussed.
   This work is supported by the National Science Foundation, grant number CBET-0854314.
Oct. 1 Madison Homecoming:
Junfang Gao
Central Care Cancer Center
Radiation therapy for cancer treatment and the potential use of  nanoparticles    Radiation therapy has been used for about 100 years in cancer treatment since X-rays were discovered. In last two decades, many cutting-edge technologies have been developed in modern radiation therapy due to the growth of the IT industry. Nanoparticles are another potential candidate to be used in cancer prevention and treatment. In this seminar, some basic radiobiology will be introduced; and traditional radiation therapy will be reviewed. Next the use of the Linear Accelerator (Linac) will be discussed. Finally nanopartilcles and their potential application in radiotherapy will be presented.
   Dr. Junfang Gao is medical physicist at Central Care Cancer Center, Bolivar, Missouri and Medical physics Consulting Group at Houston, Texas. He started his physics career in China studying General physics, Atomic physics, and Nuclear physics in 1983. He received his PhD in Molecular physics from Missouri University of Science & Technology in 2006. He worked as a post doctoral research fellow at M D. Anderson Cancer Center 2006-2008. From 2008-2009 he was a medical physics resident at Scott & White Hospital, Temple, TX.
Oct. 7
Oct. 14 Yamilov Richard Dawes
S&T's Chemistry
Automated Construction of ab initio Potential Energy Surfaces for Spectroscopy and Dynamics Applications    A molecular potential energy surface (PES) describes the energy of a chemical system as a function of geometry and is an essential ingredient for many applications of computational chemistry including spectroscopy and dynamics.  Part of this talk describes the development of a PES generator (software package) which uses parallel processing on High-Performance Computing (HPC) clusters to construct PESs automatically. Thousands of ab initio data are computed at geometries chosen by the algorithm and fit to a functional form.
   The electronic structure of molecules is difficult to describe continuously across global PESs since it changes qualitatively as bonds are formed and broken along reaction coordinates. I will discuss the development of a high-level ab initio method (GDW-MRCI) designed to allow the electronic wavefunction to smoothly evolve across the PES and provide an accurate and balanced description of the various regions.
   The methods described above have recently been applied to study the dynamics of a number of systems of interest to combustion and atmospheric chemistry. I will present results from at least two areas including comparisons with experimental measurements. The first is hyperthermal collision dynamics in which high-velocity collisions occurring in the upper atmosphere provide energy that exceeds multiple reaction barriers and leads to unusual reaction mechanisms. The second is “roaming radicals” in combustion where dissociated radical fragments of molecules such as acetaldehyde, dimethyl ether, and propane can “roam” around to ultimately form unexpected abstraction products.  If time permits, results for non-adiabatic dynamics (vibronic states) of BeC will also be presented. 
Oct. 21 Yamilov Thomas Vojta and Yew San Hor
Flat Carbon: the 2010 Nobel Prize in Physics
Oct. 28 Hor
John F. Mitchell
Argonne National Laboratory
Crystal Synthesis of Complex Oxides,
or How to Help Out Your Friendly Neighborhood Physicist
Transition metal oxides (TMO) offer the chemist, physicist or materials scientist an unprecedented opportunity to explore the full offerings of condensed matter science:  TMO lay claim to superconductors with the highest recorded transition temperature, ‘colossal’ magnetoresistors that span many decades of electrical conductivity as a function of temperature or magnetic field, negative thermal expansion solids, ferroelectrics, and the list goes on.  As materials chemists, a primary driver is to find and tailor materials that are designed to expose specific aspects of these phenomena or provide model systems for theory.  Two particularly fruitful approaches in the search for these new materials and properties are ‘phase diagram’ exploration and cation and/or anion defect control, through which a chemical constituent is varied systematically to pass through different regimes of physical behavior.   In this talk, I will discuss a few examples of this process, with an emphasis on how TMO can be ‘tricked’ into existence via synthetic artifice and then used to examine structure property relationships and fundamental physics.  Beyond new physical insights, these examples offer some ‘take-home lessons’:  beware of the so-called ‘high quality crystals,’ and big things come from small packages.
Nov. 4 Yamilov Nicholas Leventis
Missouri S&T
Assemblies of Nanoparticles as 3D Scaffolds for New Materials:
from Mechanically Strong Polymer Crosslinked Aerogels
to Porous Metals and Ceramics
Unique bulk properties such as very low thermal conductivity, low dielectric constants, high acoustic impedance, of monolithic mesoporous (>80% v/v empty space) low-density 3-D assemblies of nanoparticles known as aerogels come at a high cost: fragility. A recent breakthrough at MS&T is the development of X-aerogels where skeletal inorganic nanoparticles (e.g., silica and >30 other metal oxides) are bridged covalently by a thin conformal polymer coating that leaves the mesoporosity almost intact [1]. In essence, the inorganic framework in Xaerogels plays the role of a template for accumulation of polymer. Those 3D core-shell superstructures are true multifunctional materials with unprecedented mechanical properties that allow applications unthinkable for aerogels before (e.g., ballistic protection)....
read full abatract
Nov. 11 Yamilov Mark Havey
Old Dominion
Disorderly conduct in ultracold atomic gases
Ultracold atomic gases are presently being used to study a wide range of phenomena previously observed only in condensed matter systems. These developments are based on the capability, in ultracold gases, to finely control many aspects of the physics, including interparticle interactions and disorder. Recent experiments and theoretical results on Anderson localization of light in condensed samples show that diffusive transport is strongly suppressed and that a regime of anomalous diffusion develops dynamically. Proximity of the light localization threshold can be detected through time evolution of either forward or diffusely scattered light. In this presentation I give an overview of the general subject and the current interest in it, including the attractive features of studying ultracold atomic gases. I will first discuss light scattering in ultracold atomic rubidium samples in the weak localization regime, where multiple coherent light scattering can be thought of in terms of chains of scattering and propagation segments. This will be followed by presentation of newer results at much higher densities, in the generally expected vicinity of the localization transition. This research is supported by the National Science Foundation.
Nov. 18 Vojta Nayana Shah
University of Cincinnati
When the good old superconductors go nano: to be or not to be, that is the question Just as superconductivity is one of the most spectacular and ubiquitous emergent states of matter, it is also a classic prototype of a quintessential quantum many-body phenomenon. As we approach the hundredth anniversary of its discovery, we find ourselves in the midst of the nano-age in which quantum size effects occupy the center stage. It thus seems like an opportune time to pose the age-old question: to be or not to be?
   When the diameter of a superconducting wire shrinks down to the nanometer scale, thermal and quantum phase slips (topological fluctuation events that impart a non-zero intrinsic resistance) challenge the very existence of superconductivity. This existential question becomes sharper when the nanowire is subjected to pair-breaking perturbations---such as magnetic fields or impurities and bias currents---that are detrimental for superconductivity. After setting the stage, we will seek some answers as I sketch the recently developed theoretical pictures of stochastic switching and quantum phase transitions from the superconducting to the normal state. Our exploration will be guided by experimental measurements on superconducting nanowires (fabricated, e.g., by carbon-nanotube or DNA molecular templating) and I shall hope to have, along the way, impressed upon the audience that nanowires provide an ideal setting to systematically study quantum phase transitions, quantum-fluctuations and dissipation, all at the nano-scale. Touching upon more examples of superconducting nanostructures and the overall technological promise of superconducting nano-circuitry, I will conclude that nano-scale superconductivity is indeed a place `to be'.
Dec. 2 Yamilov Seventeen Annual Laird D. Schearer Prize Competition
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