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Physics Colloquium


Spring 2014 Colloquium Schedule

Date Speaker Title Host
January 13 Harold P. Erickson
Duke University Medical Center, Department of Cell Biology
How FtsZ assembles the Z ring and generates a constriction force to divide bacterial cells Jaan Mannik
January 20 MLK Day Holiday No Colloquium NA
January 27 Philip W. Phillips
Department of Physics
University of Illinois
Are high-temperature superconductors full of unparticles? Norman Mannella
February 3 Ethan Hull
Germanium gamma-ray detectors: from spectroscopy to imaging Norman Mannella
February 10 Nelson Christensen
Department of Physics and Astronomy
Carleton College
Detecting gravitational waves: advanced LIGO Tony Mezzacappa
February 17 James Brooks
Department of Physics
Florida State University
Interdisciplinary materials science: rubber bands, spiders, Fermi surfaces and d-electrons Haidong Zhou
February 24 Mona Berciu
Department of Physics and Astronomy
University of British Columbia
A new paradigm for polaronic behavior Steve Johnston
March 3 David Allard
Pennsylvania Bureau of Radiation Protection
Pennsylvania’s TENORM experiences and studies of the oil and gas industry Joe Macek
March 10 Raph Hix
University of Tennessee Physics
Core collapse supernovae and their nucleosynthesis  
March 17 Spring Break No Colloquium NA
March 24 Jaime Fernandez-Baca
Oak Ridge National Laboratory
Neutron scattering at Oak Ridge National Laboratory: application to the study of multiferroic materials  
March 31 Robert McKeown
Jefferson Lab
Jefferson Lab science: today and tomorrow Nadia Fomin
April 7 Bing Qi
Oak Ridge National Laboratory
Quantum cryptography using untrusted measurement device George Siopsis
April 14 Samuel Werner
NIST Neutron Physics Group
The effect of the Earth’s gravity and rotation onthe quantum mechanical phase of the neutron Geoff Greene
April 21 Warren Pickett
University of California, Davis
Superconductivity and two-dimensionality. An instance of science diplomacy in the Islamic Republic of Iran TBA
April 28 Physics Honors Day Warren Keller, 2014 Distinguished Alumni Award Winner, will speak on his career at NASA NA


January 13, 2014

Harold P. Erickson
James B. Duke Professor, Department of Cell Biology
Duke University Medical Center

How FtsZ assembles the Z ring and generates a constriction force to divide bacterial cells

FtsZ is a bacterial protein that forms a ring at the center of the cell. This Z ring constricts to pinch the bacterial cell in two. We have made a major advance by reconstructing the Z ring inside liposomes (artificial bacterial membranes) from purified FtsZ. Remarkably, these in vitro Z rings can generate a constriction force without the need for any motor protein. (This is in contrast to how animal cells divide, where actin filament sliding is driven by myosin motors.) How does FtsZ generate the constriction force? We propose a novel mechanism – the basic self-assembly of FtsZ is a protofilament, 5 nm wide by 200 nm long, that can switch from a straight to a curved conformation. The curving protofilaments generate a bending force on the membrane that results in constriction. A key element of this mechanism is the mechanical rigidity of proteins and their polymers. Proteins are not “soft wet materials.” Microtubules and FtsZ protofilaments have a Young’s modulus of 1.2 gPa, similar to hard plastic like Plexiglas. A challenge remains to determine how the short, curving FtsZ protofilaments actually transmit force and distort the lipid bilayer membrane to generate the constriction.

January 27, 2014

Philip W. Phillips
Professor, Department of Physics
University of Illinois

Are high-temperature superconductors full of Unparticles?

I will begin this colloquium by using the standard procedure in condensed matter to count particles. For strongly correlated models relevant to high-temperature superconductors, I will show that this procedure cannot account for all the charged degrees of freedom. The charged stuff which is left out cannot be given an interpretation in terms of particles. I will argue that the unparticle construction of Howard Georgi's makes up the difference. I will show how a gravity dual can be used to determine the scaling dimension for unparticles.

I will close by elucidating a possible superconducting instability of unparticles and demonstrate that unparticle stuff is likely to display fractional statistics in the dimensionalities of interest for strongly correlated electron matter.

February 3, 2014

Ethan Hull
Knoxville, Tennessee

Germanium gamma-ray detectors: from spectroscopy to imaging

Germanium semiconductor gamma-ray detectors have provided the best gamma-ray spectroscopy for the past four decades. A unique and fortuitous combination of physical properties enables the fabrication of large germanium diodes that function as excellent gamma-ray detectors when cooled to the liquid-nitrogen temperature region. The detector contacts can be segmented to provide spatial resolution. Together, the spatial and energy resolution can be used for nuclear physics research and gamma-ray imaging applications. The physics of charge-carrier collection, signal induction, detector fabrication, crystal growth and gamma-ray imaging are described.

February 10, 2014

Nelson Christensen
Department of Physics and Astronomy
Carleton College

Detecting Gravitational Waves: Advanced LIGO

Gravitational wave detection with laser interferometric detectors will be presented. Specifically, the strategies, results and goals of the Laser Interferometric Gravitational-wave Observatory (LIGO) will be given. Interesting gravitational wave sources will be described. Results from signal searches with initial LIGO will be summarized. Advanced LIGO, with a factor of 10 better sensitivity, will soon be coming on-line. Advanced LIGO will be described, and the potential signal sources expected to be observed will be given.

February 17, 2014

James Brooks
Physics Department and National High Magnetic Field Laboratory
Florida State University

Interdisciplinary Materials Science: Rubber Bands, Spiders, Fermi Surfaces and d-electrons

Materials science is becoming ever more diverse and interdisciplinary, with new materials and new experimental capabilities constantly advancing; for many of us this is a very exciting time for education and research. In this presentation, directed at a general audience, I will review some of the activities and projects that are currently underway at Florida State University and the National High Magnetic Field Laboratory, spanning topics from high school to graduate school, and from soft to hard matter.

February 24, 2014

Mona Berciu
Department of Physics and Astronomy
University of British Columbia

A new paradigm for polaronic behavior

Any charge carrier distorts the lattice in its neighborhood because of interactions with the ions making up the crystal (electron-phonon interactions). This results in a dressed quasiparticle, or a polaron, which is the composite object comprising the carrier and this lattice distortion that can be viewed as a cloud of phonons (quantized lattice vibrations) that are continuously absorbed and re-emitted by the carrier. This cloud may lead to a significant renormalization of the properties of the quasiparticle compared to those of the bare carrier, which is why understanding the properties of polarons and their influence on the macroscopic behavior of the host material is one of the main challenges in condensed matter physics. The widely-accepted "polaron paradigm" is that stronger electron-phonon coupling leads to bigger lattice distortions and therefore heavier polarons. In this talk I present recent work which shows that this is true only for models where the phonons modulate the potential energy of the carrier. If the phonons modulate the kinetic energy of the carrier one may find very light polarons at any coupling. The reason for this and other surprising findings will be explained.

March 3, 2014

David J. Allard
Pennsylvania Bureau of Radiation Protection

Pennsylvania’s TENORM Experiences and Studies of the Oil and Gas Industry

This presentation will provide an overview of the Commonwealth of Pennsylvania’s experiences and ongoing studies related to technologically enhanced naturally occurring radioactive material (TENORM) in the oil and gas industry. It has been known for many years that Pennsylvania’s geology is unique, with several areas having relatively high levels of natural uranium and thorium in surface rock formations. In the 1950s a few areas of the state were evaluated for commercial uranium production. In the late 1970s scoping studies of radon in homes prompted PA’s Bureau of Radiation Protection (BRP) to begin planning for a larger state-wide radon study. The BRP and Oil & Gas Bureau also performed a TENORM study of produced water in the early 1990s for a number of conventional oil and gas wells. More recently BRP and the Bureau of Solid Waste developed radiation monitoring regulations for all PA solid waste transfer and disposal facilities. These were implemented in 2001 prompting another evaluation of oil and gas operations and sludges generated from the treatment of conventional produced water and brine, but mainly focused on the disposal of TENORM solid waste in the state’s RCRA Subtitle D landfills. However since 2008 the increase in volumes of unconventional gas well wastewater has compelled DEP to fully re-examine these oil and gas operations. This is due to the increase in wastewater volumes and levels of radium-226 observed in the shale gas well flow-back frac water. Specifically, with BRP in the lead, a new TENORM study of oil and gas operations and related wastewater treatment operations has been initiated. This study began in early 2013, and will examine the potential public and worker radiation exposure, environmental impact, as well as re-evaluate TENORM waste disposal. This presentation will provide an overview of: PA’s geology and respective uranium / thorium content, conventional and unconventional oil and gas well operations, radium content in oil and gas wastewater, treatment solids, radon in natural gas, the scope of other TENORM issues in the state, regulatory framework, national regulations and guidance, and provide a summary of past, and status of ongoing, TENORM studies in the Commonwealth.

March 10, 2014

Raph Hix
University of Tennessee Department of Physics and Astronomy

Core Collapse Supernovae and their Nucleosynthesis

Core-collapse supernovae, the culmination of massive stellar evolution, are among the brightest and most powerful explosions in the universe and are the principle actors in the story of our elemental origins. Our developing paradigm for the initiation of a core-collapse supernova reveals a supernova shock that stalls for hundreds of milliseconds before reviving. Though brought back to life by neutrino heating, the development of the supernova is inextricably linked to three dimensional fluid flows, with large scale hydrodynamic instabilities allowing successful explosions that spherical symmetry would prevent. Unfortunately, our understanding of the nucleosynthesis that occurs in these explosions, and their impact on galactic chemical evolution, is based on spherically symmetric simulations with parameterized explosions, ignoring much that we have learned about the central engine of these supernovae over the past two decades. I will present recent results from two and three dimensional simulations of core-collapse supernovae using the CHIMERA code and discuss how the multi-dimensional character of the explosions directly impacts the nucleosynthesis and other observables of core-collapse supernovae.

March 24, 2014

J. A. Fernandez-Baca
ORNL Quantum Condensed Matter Division

Neutron Scattering at Oak Ridge National Laboratory: Application to the study of Multiferroic Materials

Neutrons have unique properties that make them an ideal probe of condensed matter systems. They have wavelengths and energies comparable to the typical atomic distances and collective excitations in solids, making them suitable to study the crystalline structures and the dynamics of materials. They have no electric charge which gives them the ability to penetrate to the bulk of most materials. Neutrons also have a magnetic moment which makes them very useful to study the magnetic structures and magnetic excitations in magnetic materials. In this talk I will present a brief history of neutron scattering and describe the properties that make neutrons unique to study materials. I will also present examples of recent research in the study novel materials and discuss the opportunities of scientific research, mentoring and training at the US: the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. In particular I will present recent results in the study of multiferroics, materials that attracted considerable attention because of their large magnetoelectric effect and their potential use in electronic devices. I will show that neutrons are ideal to probe the spin arrangements and the nature of the magnetic interactions in these materials. I will present a neutron scattering study on MnWO4, a multiferroic material whose magnetic structure is driven by magnetic frustration and long range interactions; and the more recent study on (Y-Lu)MnO3 where the magnetoelectric effect can be tuned by changing the degree of the trimerization distortion of Mn ions.

March 31, 2014

Robert McKeown
Jefferson Lab

Jefferson Lab Science: Today and Tomorrow

The continuous electron beam accelerator facility at Jefferson Lab, built with advanced superconducting radiofrequency (SRF) technology, provides opportunities to discover fundamental new aspects of the structure of visible matter – protons, neutrons and other bound states, and of the strong interaction, described by the gauge theory Quantum Chromodynamics. Jefferson Lab’s accelerator, in operation since 1995, is unique in the world and is currently undergoing a major upgrade to double its energy. The upgrade will bring new opportunities, not only in the study of hadronic matter, but also in searches for new physics, such as a suite of experiments to search for massive “dark photons”. In this talk, I will give an overview of Jefferson Lab’s current and future science program, including an outlook for the future of the laboratory.

April 7, 2014

Bing Qi
Oak Ridge National Laboratory

Quantum cryptography using untrusted measurement device

Nowadays, as internet and electronic business grow ever more popular, cryptography has become an essential part of our everyday life. Built upon the fundamental laws of quantum mechanics, quantum cryptography (QC), in theory, offers unconditional security (i.e., security against any eavesdropper with unlimited computing power and technological capabilities). However, imperfections in real-life implementations of QC may open a possibility for “side-channel” attacks and thus compromise its unconditional security. Indeed, quantum hacking against practical QC systems, particularly via detector side-channel attacks, has emerged as a hot topic.

In this talk, I will present the basic idea behind quantum key distribution (QKD) protocol – arguably the most mature technology in quantum cryptography. I will demonstrate how one can prove its security without knowing what the eavesdropper does. I will also review a few successful quantum hacking schemes and show how small imperfections ignored in the security proof could spoil the security of the whole system. Finally, I will discuss a promising solution to detector side-channel attacks, the so-called measurement-device-independent QKD (MDI-QKD) protocol, which allows QKD users to establish a secure key without trusting their measurement device. This is remarkable because it means that the most expensive and complicated part in a QKD system would no longer require any special security certifications and, in fact, they can even be manufactured and fully controlled by a malicious eavesdropper.

April 14, 2014

Sam Werner
Neutron Physics Group, NIST

The effect of the Earth’s gravity and rotation on the quantum mechanical phase of the neutron

Does Einstein’s principle of equivalence of inertial and gravitational masses apply in the quantum limit? This question was posed and experimentally addressed in the neutron interferometry experiment of Colella, Overhauser and Werner (COW) in 1975. I will discuss this and subsequent versions and extensions of this experiment, and how they impact the recent controversy related to the gravitational redshift and Compton frequency in atomic-beam interferometry.

April 21, 2014

Warren E. Pickett
University of California, Davis

Superconductivity and Two-dimensionality. An instance of science diplomacy in the Islamic Republic of Iran

“In looking at the various classes of high temperature superconductors, one is struck by the near dominance of (quasi)two dimensional (2D) materials: the HTS cuprates with Tc up to 130K (or 160+ K under pressure); the iron-based superconductors (up to 56K); MgB2 (40K). In this lower range of high temperature superconductors falls two classes of 3D materials: the fullerides A3C60 (A=alkali elements; Tc up to 40K) and (Ba,K)BiO3 (30 K). The next highest Tc superconducting class is that of the electron-doped (Zr,Hf)NCl system, with Tc up to 26K. This lecture will focus on 2D aspects of electronic and magnetic structure that are candidates to be related to superconducting pairing in several of these systems, with references to attempts to “design” new, better superconductors (so far unsuccessfully). The mysterious Lix(Zr,Hf)NCl system, where pairing is not magnetic and apparently not normal phononic, will receive specific attention in this presentation.”

This abstract presaged a talk given at the 4th National Conference on Advanced Superconductivity, 6-7 February 2014 at the Sharif University of Technology, Tehran. In addition to a slightly condensed version of this talk, I will spend several minutes relating my experiences during a two week visit in February 2014 to four universities (and several tourist sites). During this pleasant and rewarding visit, my two colleagues and I were indulging in a practice called “science diplomacy” that is gaining adherents in recent years.

Previous Physics Department Colloquia


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