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Physics Colloquium


Fall 2015 Colloquium Schedule

Date Speaker Title Host
August 24 Steve Abel
UTK Chemical and Biomolecular Engineering
Contact-Mediated Spatial Organization of Membranes

Tony Mezzacappa
August 31 Seunghun Lee
University of Virginia
Spin Jam Induced by Quantum Fluctuations in a Frustrated Magnet Haidong Zhou
September 7 Labor Day Holiday: No Colloquium NA NA
September 14 Timothy Gay
University of Nebraska, Lincoln
Football: Its Physics and Future Geoff Greene
September 21 Richard Wigmans
Texas Tech
Neutrinos in an Expanding Universe Yuri Kamyshkov
September 28 Jané Kondev
Brandeis University
The Physical Genome Jaan Mannik
October 5 André de Gouvêa
The Brave Nu World Yuri Kamyshkov
October 12 Eric Braaten
Ohio State University
Ultracold Atoms: How Quantum Field Theory Invaded Atomic Physics Lucas Platter
October 19 Raph Hix
  Tony Mezzacappa
October 26 Naoko Kurahashi Neilson
Drexel University
Detecting Cosmic Neutrinos with IceCube at the Earth's South Pole Nadia Fomin
November 2 Hiroyoshi Sakurai
  Robert Grzywacz
November 9 Nicholas D. Scielzo
Lawrence Livermore National Laboratory
  Robert Grzywacz
November 16 Mark Fitzsimmons
Stress and Charge—Routes to Perfect Synthetic Magnetoelectric Coupling across Interfaces Hanno Weitering
November 23 Chen-Yu Liu
Indiana University
  Yuri Kamyshkov
November 30 Peter Abbamonte
University of Illinois
  Adolfo Eguiluz


August 24, 2015

Contact-Mediated Spatial Organization of Membranes
Steve Abel, UTK Chemical and Biomolecular Engineering

Intercellular communication is often facilitated by direct physical contact between cells, with receptor-ligand recognition at the cell-cell interface triggering cell signaling and response. Such communication involves a complex interplay between molecular binding, membrane organization and mechanics, and cytoskeletal interactions. In this talk, we use theoretical and computational methods to explore problems in which receptor binding and the actin cytoskeleton influence membrane organization and shape. We first study the binding and subsequent spatial reorganization of complementary molecules on apposed membranes. When two or more molecular complexes with different natural lengths are present, the species segregate into distinct spatial regions, even in the limit of vanishing membrane surface tension and bending rigidity. We then study actin in confined membrane environments such as vesicles and membrane nanotubes. Bundles of actin filaments can significantly deform the surrounding membrane and may stabilize membrane nanotubes by suppressing membrane shape fluctuations. Our approach to these problems is linked by a theoretical framework rooted in statistical mechanics and is part of our larger research program exploring the spatiotemporal dynamics of membrane-proximal events in cells.

August 31, 2015

Spin Jam Induced by Quantum Fluctuations in a Frustrated Magnet
Seunghun Lee, University of Virginia

Can a glassy state exist in the absence of defects? This long-standing problem in condensed matter physics will be addressed in this talk by discussing glassy states found in frustrated magnets. Recently, we found that although classically the ground state of a strongly frustrated magnet is a spin liquid, quantum corrections can break the classical degeneracy into a set of aperiodic spin configurations forming local minima in a rugged energy landscape. A consequence of the complex energy landscape is that, upon cooling, the system gets trapped in one of the local minima, leading to a glassy state that we call a spin jam.[1] I will present our recent experimental work on SrCr_{9p}Ga_{12-9p}O_{19} (SCGO(p)) that revealed existence of a unique spin jam state in the vicinity of the clean limit, which strongly support the possible existence of purely topological glassy states.[2]

[1] I. Klich, S.-H. Lee, K. Iida, Nature Comm. 5, 3497 (2014).
[2] J. Yang et al., PNAS, In Press (2015).

September 14 , 2015

Football: Its Physics and Future
Timothy J. Gay, University of Nebraska

The game of American Football is under assault. There are several reasons for this: the media have recently discovered that football is a violent game, there are a diminishing number of jobs available for the graduates of our law schools, and our scientific understanding of concussions has improved from complete ignorance to a vague resemblance of comprehension. This talk will discuss the physics and physiology of football-related concussions and their mitigation, the history of anti-football campaigns of the past, and the future of the game itself in light of the many sociological and scientific forces aligned to end it.

September 21 , 2015

Neutrinos in an Expanding Universe
Richard Wigmans, Texas Tech University

Colloquium File | Neutrinos in an Expanding Universe Paper (IOP) | PeV Cosmic Rays: a Window on the Leptonic Era?

The Universe contains several billion neutrinos for each nucleon. In this talk, we follow the history of these relic neutrinos as the Universe expanded. At present, their typical velocity is of the order of hundred km/s and, therefore, their spectra are a ected by gravitational forces. This may have led to a phenomenon that could explain two of today's great mysteries: The large-scale structure of the Universe and the increasing rate at which it expands. In addition, relic neutrinos o er an elegant explanation for some features of the high- energy cosmic ray spectrum, namely the \knees" and the sudden changes in chemical composition observed at 5 and 300 PeV. Relic neutrinos may also be a major component of the dark matter halos of galaxies. All the above statements hinge critically upon the value of the neutrino restmass, which is one of the most crucial missing ingredients of the Standard Model of particle physics.

September 28 , 2015

The Physical Genome
Jané Kondev, Brandeis University

Every day there seems to be a story in the news about DNA and the genes that it encodes. While this abstraction of DNA as an information storage device is dominant in modern biology, in this talk I will consider the physical nature of DNA. Namely, DNA is a long, flexible, negatively charged molecule and its physical properties affect a number of critical functions that it performs in the cell. One such function is to turn on and off the production of proteins, which are the building blocks of the cell, in response to different physical and chemical cues. Another is to repair itself when it is broken. In this talk I will describe how simple physics models combined with experiments on cells and single molecules are being used to develop a quantitative understanding of the physical genome.

October 5 , 2015

The Brave Nu World
André de Gouvêa, Northwestern University

Colloquium Slides

Nonzero neutrino masses are the most concrete evidence of physics beyond the standard model to date. I will provide an overview of the current status of neutrino physics, concentrating on recent developments. I will also discuss outstanding experimental and theoretical issues, and the program that is required in order to fully explore the neutrino mass puzzle, which ranges from precision neutrino oscillation searches to searches for charged-lepton flavor violation to the pursuit of a finite proton lifetime.

October 12 , 2015

Ultracold Atoms: How Quantum Field Theory Invaded Atomic Physics
Eric Braaten, Ohio State University

The development of the technology for trapping atoms and cooling them to ultralow temperatures gave birth to a new subfield of atomic physics. It also led to the introduction of new theoretical methods into atomic physics, in particular quantum field theory (QFT). I will describe the QFT's relevant to ultracold atoms. A unique aspect of ultracold atoms is that their interactions can be tuned experimentally and made arbitrarily large (or small). When the interaction strength is infinitely large, the interactions do not provide any length scale and are described by a nonrelativistic conformal QFT. I will describe a new concept, the contact, and a new condensed matter system, the unitary Bose gas, that have emerged from studies of ultracold atoms.

October 26, 2015

Detecting Cosmic Neutrinos with IceCube at the Earth's South Pole
Naoko Kurahashi Neilson, Drexel University

The universe has been studied using light since the dawn of astronomy, when starlight captured the human eye. The IceCube Neutrino Observatory observes the universe in a different and unique way: in high-energy neutrinos. IceCube's recently discovery of a diffuse flux of astrophysical neutrinos, in other words, neutrinos from beyond the solar system, started a new era of neutrino astronomy. I will motivate why neutrinos are a necessary messenger in high-energy astronomy. I will discuss the multiple diffuse flux analyses in IceCube that observe the astrophysical flux, and what each can tell us. Spatial analyses that aim to identify the sources of such astrophysical neutrinos will also be discussed, followed by an attempt to reconcile all results, to draw a coherent picture that is the state of neutrino astronomy.

November 16, 2015

Stress and Charge—Routes to Perfect Synthetic Magnetoelectric Coupling across Interfaces
M.R. Fitzsimmons, Oak Ridge National Laboratory, Quantum Condensed Matter Division

Novel electric and magnetic properties can be achieved in materials engineered at nanometer dimensions. Examples include conducting or magnetic interfaces between materials that are neither conducting nor magnetic. New functionality stems from the atomic, magnetic or charge/orbital structure of the interface. With an understanding of interface structure, electric and magnetic degrees of freedom may be controlled, ideally at room temperature, to achieve synthetic magnetoelectric coupling in a nanocomposite. In this talk I describe applications of polarized neutron reflectometry (PNR) and X‐ray resonant magnetic scattering (XRMS) to probe magnetic interfaces in heterostructures and nanocomposites. One application reports the response of magnetism in (La0.4Pr0.6)0.67Ca0.33MnO3 (LPCMO) and La0.8Sr0.2MnO3 (LSMO) thin films to applied bending stress. We find compressive bending stress, exclusive of all other factors, favors ferromagnetism in LPCMO films. In addition, the metal-insulator-transition maybe a consequence of two-dimensional percolation, regardless of applied stress. A second application illustrates the use of XRMS to test the hypothesis that magnetization can be changed through hole doping of a LSMO/ferroelectric interface. We find evidence to support the hypothesis, although our results are not fully consistent with a recently published study. I conclude with a discussion of PNR and small angle neutron scattering experiments that demonstrate two methods to control electricity and magnetism by synthesizing magnetoelectric coupling across interfaces.

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