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Physics Colloquium

 

Fall 2016 Colloquium Schedule

Date Speaker Title Host
August 22 Kate Jones
UT Physics
Direct reaction experimental studies with beams of radioactive tin ions  
August 29 Shina Tan
Georgia Institute of Technology
Quantum behavior of extremely cold atoms Lucas Platter
September 5 Labor Day Holiday No Colloquium NA
September 12 CANCELLED    
September 19 Brian Fields
University of Illinois at Urbana–Champaign
When stars attack! Near-Earth supernova explosion threat and evidence Raph Hix
September 26 James Lattimer
Stony Brook University
Constraining the physics of dense matter with neutron stars Andrew Steiner
October 3 Chang Cen
West Virginia University
Nanoscale manipulations of the structural and electronic phases of vanadium oxides Jian Liu
October 10 Joseph Silk
Oxford
Challenges in cosmology from the Big Bang to dark energy, dark matter and galaxy formation Jirina Stone
October 17 Jaan Mannik
UT Physics
Self-organization of bacterial chromosomes and cell division apparatus  
October 24 Suzanne Lapi
University of Alabama, Birmingham
From isotopes to images: accelerator production of radionuclides for nuclear medicine Kate Jones
October 31 Kate Scholberg
Duke University
What stubs and sparkles in vast vats of liquid will tell us about exploding stars Nadia Fomin
November 7 Peter Winter
Argonne National Laboratory
Muon g-2 at Fermilab: finding the right moment Lucas Platter
November 14 Collin Broholm
Johns Hopkins University
Strange magnetism exposed by neutron scattering Haidong Zhou
November 21 Wei Guo
Florida State University
Understanding quantum hydrodynamics: flow visualization in superfluid helium-4 Mike Fitzsimmons
November 28 Ruxandra Dima
University of Cincinnati
Multi-scale modeling of the nanomechanics of biomolecular
assemblies
Jaan Mannik

Abstracts

August 22

Direct reaction experimental studies with beams of radioactive tin ions

Kate Jones, University of Tennessee Department of Physics and Astronomy

Just as atoms have a well-dened structure of orbits, atomic nuclei have a shell structure in which nuclei with "magic numbers" of neutrons and protons are analogous to the noble gases in atomic physics. Knowledge of the properties of single-particle states outside nuclear shell closures and aware from the valley of stability is important for a fundamental understanding of nuclear structure and nucleosynthesis. Over the past decades, nuclear physicists have vastly improved their abilities to fabricate and characterize short-lived nuclei with large imbalances of neutrons and protons. These rare isotopes, where rare can be dened as both, "not native to the place where they are found", and "strikingly, excitingly, or mysteriously dierent or unusual" [1] are created in primary reactions, or decays, and may then be ltered, and in some cases reaccelerated, to produce a Rare Ion Beam (RIB). Direct reaction techniques, such as transfer and knockout reactions, are powerful tools to study the single-particle nature of nuclei. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. The tin chain of isotopes is a unique example, with the largest number of stable isotopes of any element, it stretches from doubly-magic 100Sn, through double-magic 132Sn and beyond, into the region of the astrophysical r-process path. Examples of direct reaction experiments with both neutron-rich and neutron-decient tin beams will be presented.
[1] Merriam-Webster Dictionary.


August 29

Quantum behavior of extremely cold atoms

Shina Tan, Georgia Institute of Technology

To our knowledge, by far the coldest places in the universe are on Earth. When atomic vapors are cooled to something like a billionth of a degree above absolute zero, things get simplified since the de Broglie wave lengths of atoms are now enormous, and atoms behave like point particles. Using the technique of Feshbach resonance, people can still make them interact with each other strongly. I will discuss some weird quantum behavior of these strongly interacting atoms, as well as some exact theoretical results.


September 19

When stars attack! Near-Earth supernova explosion threat and evidence

Brian Fields, University of Illinois at Urbana-Champaign

The most massive stars are the celebrities of the cosmos: they are rare, but live extravagantly and die in spectacular and violent supernova explosions. These awesome events take a sinister shade when they occur close to home, because an explosion very nearby would pose a grave threat to Earthlings. We will discuss these cosmic insults to life, and ways to determine whether a supernova occurred nearby over the course of the Earth's existence. We will present evidence that one or more stars exploded near the Earth about 3 million years ago. Radioactive iron atoms have been found globally in deep-ocean material, and very recently reported in lunar samples as well. These are supernova debris, transported to the Earth as a "radioactive rain." With these data, for the first time we can use sea sediments and lunar cores as telescopes, probing the nuclear fires that power exploding stars and possibly even indicating the direction towards the event(s). Furthermore, an explosion so close was probably a "near-miss" that exposed the biosphere to intense and possibly harmful ionizing radiation.


September 26

Constraining the physics of dense matter with neutron stars

James Lattimer, Stony Brook University

The structure of neutron stars, for example their radii and moments of inertia, depend on the symmetry properties of the nuclear interaction in the vicinity of the nuclear saturation density. Thus, limits to symmetry properties from nuclear measurements and theoretical neutron matter calculations provide very important constraints on neutron stars and dense matter. New precision measurements of high-mass neutron stars, coupled with general relativity, enhance these constraints. Although measurements of neutron star radii through astronomical observations are not yet precise enough, anticipated measurements of thermal emission using the Neutron Star Interior Composition ExploreR (NICER), moments of inertia from pulsar timing observations, gravitational waves from neutron star mergers, and supernova neutrinos all have the potential of testing and refining these predictions.


October 3

Nanoscale manipulations of the structural and electronic phases of vanadium oxides

Chang Cen, West Virginia University

The capability of generating sharp material contrasts in small length scales is the major enabler of high performance electronic and photonic devices. Here we show that the transitions between three distinct VO2 based material phases can be controlled in nanoscale by conducting atomic force microscope (c-AFM). Such result was achieved by field ionization of the spontaneously formed water meniscus at probe-sample junction and the resultant localized ion reactions with VO2. The three phases, including two close-packed structures with monoclinic/rutile-like lattices and a layered structure with Van der Waals interlayer coupling, differ not only structurally but also in their metallicity and optical properties. Using the c-AFM writing technique, arbitrary nano-patterns of the three phases as well as their in-plane heterostructures can be deterministically created, which is highly useful for producing advanced multifunctional device architectures on demand.


October 10

Challenges in cosmology from the Big Bang to dark energy, dark matter and galaxy formation

Joseph Silk, Oxford University

I review the current status of Big Bang Cosmology, with emphasis on current issues in dark matter, dark energy, and galactic structure formation. These topics motivate many of the current goals of experimental cosmology which range from targeting the nature of dark energy and dark matter to probing the epoch of the first stars and galaxies.


October 17

Self-organization of bacterial chromosomes and cell division apparatus

Jaan Mannik, University of Tennessee Department of Physics and Astronomy

Bacterial cells, despite their apparent simplicity, maintain a highly organized structure of DNA and membrane-bound proteins. How nanometer-scale proteins and chromosomal domains position accurately within micron-scale bacteria intrigues both biologists and physicists. A critical process requiring precise protein localization is cell division. In most bacteria, localization of cell division proteins is controlled by self-assembly of the FtsZ proteins into filamentous ring-like structure, the Z-ring, which encircles the cell at its middle. In Escherichia coli, research carried out over the past several decades has determined two independent molecular mechanisms that are involved in the midcell placement of the Z-ring. The two mechanisms operate by negatively regulating formation of the Z-ring in certain regions of the cell. We have recently found an additional positioning system that controls localization of the Z-ring in the cell by a positive regulation. The underlying molecular system directs assembly of cell division proteins to the vicinity of chromosomal replication terminus region. Thus, the bacterial chromosome in addition to carrying genetic information also acts as a structural scaffold for cell division proteins. Interestingly, chromosomal positioning itself seems to be to a large degree irreducible and independent of other systems. Our modelling shows that entropic force alone is capable of organizing bacterial chromosome in a cylindrical cell. The second law of thermodynamics thus reveals itself as an organizing principle in such complex and non-equilibrium system as is the bacterial cell.


October 24

From isotopes to images: accelerator production of radionuclides for nuclear medicine

Suzanne E. Lapi, Cyclotron Facility Director and Associate Professor
Department of Radiology, University of Alabama at Birmingham

The drive towards personalized medicine to enable patient specific treatment plans has spurred interest in the next generation of diagnostic imaging agents. New imaging techniques which can help physicians determine which patients are likely to respond to which therapy are critical for success. In particular radiopharmaceuticals suitable for positron emission tomography (PET) imaging have shown to be important tools in this area and has led to the development of new accelerator targetry and separation techniques for isotope production. For example, the production and purification of longer-lived position emitting radionuclides has been explored to allow for nuclear imaging agents based on peptides, antibodies and nanoparticles. These isotopes (55Co, 89Zr, 52Mn and others) are produced via irradiation of solid targets on the UAB 24 MeV cyclotron. Research pertaining to development of larger scale production technologies including solid target systems and remote systems for transport and purification of these isotopes has enabled both preclinical and clinical imaging research including first-in-human studies. In particular, our group has focused on the use of 89Zr radiolabeled antibodies for imaging of cell surface receptor expression in preclinical models and more recently in a clinical trial of metastatic breast cancer patients. During this seminar, isotope production strategies and the use of novel imaging agents will be discussed.


October 31

What stubs and sparkles in vast vats of liquid will tell us about exploding stars

Kate Scholberg
Department of Physics, Duke University

When a massive star collapses at the end of its life, nearly all of the gravitational binding energy of the resulting remnant is released in the form of neutrinos. I will discuss the nature of the core-collapse neutrino burst and what we can learn about particle physics and about astrophysics from the detection of these neutrinos. I will cover supernova neutrino detection techniques in general, current supernova neutrino detectors, and prospects for specific future experiments.


November 7

Muon g-2 at Fermilab: finding the right moment

Peter Winter, Argonne National Laboratory

The study of the muon -- the heavier cousin of the electron -- has undergone a big revival over the past two decades. Today the muon is used as a probe for very precise measurements to understand the electro-weak interaction and to search for new physics. In this presentation, a few general examples of the versatility of muon physics around the globe will be highlighted. The second half of the talk will focus on one prominent example of precision measurements with the muon. The new Muon g-2 experiment at Fermilab will determine the anomalous magnetic moment, g-2, of the muon to a precision of 140 parts-per-billion. This is a four-fold improvement over the former measurement performed at Brookhaven National Laboratory. The anomalous magnetic moment of the muon arises from its interaction with virtual particles in the vacuum. Within our current theoretical framework, g-2 can be calculated to a similar level of precision. The former experiment at Brookhaven and our theoretical prediction differ by 3.5 standard deviations. The new Muon g-2 experiment at Fermilab will determine if this deviation is real in which case it will be a clear sign of new physics. In order to reach this challenging precision, a 45-m circular storage ring magnet was brought from Brookhaven to Fermilab. Currently, many upgrades to the detection system are built in order to start data taking in 2017 and achieve the final precision goal.


November 14

Strange magnetism exposed by neutron scattering

Collin Broholm, The Johns Hopkins University

A radically different form of magnetism defined by quantum entanglement is explored using neutron scattering. Starting from illustrative one-dimensional examples, I discuss recent experiments that probe magnetic excitations in two and three-dimensional frustrated quantum magnets. In analogy with atomic positions in superfluid 4He, atomic scale magnetic dipoles in these materials exist in a state of quantum superposition near the absolute zero temperature. While there is no static magnetic order to distinguish such materials they host exotic emergent quasi-particles that may find use for quantum computing.


November 21

Understanding quantum hydrodynamics: flow visualization in superfluid helium-4

Wei Guo, Florida State University National High Magnetic Field Laboratory

Helium-4 has long been recognized as a useful material in fluid research. In the superfluid phase (He II), helium-4 consists of two intermiscible fluid components: an inviscid superfluid and a viscous normal fluid. This two-fluid system exhibits fascinating quantum hydrodynamics that has important scientific and engineering applications. It supports the most efficient heat-transfer mechanism (i.e. thermal counterflow), and it also allows the generation of flows with extremely high Reynolds numbers for turbulence modelling that cannot be achieved by other fluid materials. However, the lack of high-precision flow measuring tools in He II has impeded progress in understanding and utilizing its hydrodynamics. I will discuss a molecular tagging velocimetry technique that we recently developed based on the generation and imaging of thin lines of metastable He2 tracer molecules [1]. These molecular tracers are created via femtosecond-laser field ionization of helium atoms and can be imaged via laser-induced fluorescence [2]. By observing the displacement and distortion of the tracer lines in helium, quantitative information of the flow-field can be extracted. Application of this technique to heat induced flow in He II has allowed us to reveal a novel form of turbulence [3]. I will also briefly discuss our ongoing experiment with magnetically levitated helium drops. This experiment aims to produce unprecedented insight into the unexplored dynamics of rotating superfluid drops.

November 28

Multi-scale modeling of the nanomechanics of biomolecular assemblies

Ruxandra I. Dima, University of Cincinnati

Large-size biomolecular systems that assemble, disassemble, and self-repair by controlled inputs play fundamental roles in biology and are the target of numerous efforts to design intelligent materials with tunable mechanical properties. Microtubules, the largest and most rigid polymeric structures of the cytoskeleton, are assembled and disassembled where and when they are required by the cell through their interactions with a wide variety of associated proteins. The overwhelming majority of these proteins are molecular machines that convert the energy from nucleotide hydrolysis into work used to cut (sever) or depolymerize microtubules. Although experiments have shown that the severing activity itself can be regulated by a number of cellular biochemical and biophysical effectors, there is currently no work illuminating the direct mechanism of severing. That is because direct experiments measuring microtubule severing are limited in spatial and temporal resolution. I will present results of our large-scale molecular simulations using a novel self-organized polymer model, which describes the microtubule subunits at atomistic level, combined with force generation at specific positions akin to AFM indentation experiments to explore how the microtubule can be destroyed at the molecular level. Particular focus will be on new insights about the energetics of protofilaments, the origin of microtubule mechanical stability, and especially on the mechanism employed by severing enzymes to tear microtubules apart. Finally, I will discuss the validation of these results through direct comparison with in vitro experiments, indicating that the measured parameters sample the same distributions.


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