|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
|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||TBA|
|March 17||Spring Break||No Colloquium||NA|
|March 24||Jaime Fernandez-Baca
Oak Ridge National Laboratory
|March 31||Robert McKeown
|April 14||Samuel Werner
NIST Neutron Physics Group
|April 21||Warren Pickett
University of California, Davis
|April 28||Physics Honors Day||TBA||NA|
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.
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.
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.
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.
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.
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.
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.
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.
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