Fall 2009 Physics Colloquium Schedule

University of Colorado Department of Physics

Colloquia are Wednesdays at 4 PM, Duane G-1B20 unless otherwise noted

Coffee, tea, and cookies before regular colloquia at 3:45 PM in Duane G-1B31

Upcoming Colloquia:

• November 11
  • Tune Kamae, SLAC National Accelerator Laboratory
  • Host: Uriel Nauenberg
  • Title: Physics We Learned from the First Year Observations with Fermi
  • Abstract: Fermi Large Area Telescope (Fermi LAT) has been surveying all sky since August 2008. In the past 16 months, there ~15 billion events passed onboard filtering and sent to the ground of which ~200 million gamma-ray candidates have been found by the reconstruction program. We know almost all gamma rays are produced by high energy particles accelerated in some astronomical objects. The talk will focus on two topics: what we have learned about particle acceleration mechanisms and where we are searching for the dark matter signal. On the first topics, we are closing on the gamma-ray emission mechanism in the rotating neutron pulsars and on the pion production mechanism in the middle-aged Galactic supernovae. On the dark matter search front, we have been studying one-by-one what conventional models predict and looking for a statistically significant "excess" that will require a new physics including dark-matter annihilation.
• November 18
  • Neil Ashby and Peter Bender, University of Colorado and JILA
  • Host: John Wahr
  • Title: Testing Relativity: the BepiColombo Mission, the Laser Interferometer Space Antenna, and a Proposed Shapiro Time Delay Measurement
  • Abstract: Three space missions with the potential to make important improvements in tests of general relativity will be discussed. One is the BepiColombo mission to Mercury planned for launch by the European Space Agency (ESA) in 2013. A high-accuracy microwave ranging transponder system on the BepiColombo Mercury Planetary Orbiter will make possible improved tests based on Earth-Mercury distance variations over a period of one to two years. The second mission is the Laser Interferometer Space Antenna (LISA), which is being planned as a joint ESA-NASA mission. It should give extremely precise tests of gravitational theory for the emission of gravitational waves under highly relativistic conditions. A third possible future mission could provide a much improved measurement of the gravitational time delay and hence of the important PPN parameter gamma for laser beams passing near the Sun. It would require the space qualification of a very stable optical clock, such as the types that are being developed at NIST and at the University of Colorado.
• November 25
  • Fall Break, no Colloquium
• December 2
  • Mayly Sanchez, Iowa State University
  • Host: Alysia Marino
  • Title: Measuring the Elusive: Neutrino Oscillations in MINOS and Beyond
  • Abstract: Since neutrino oscillations were observed and announced to the World in 1998, the field of neutrino physics has been teeming with activity. A forefront contributor is the MINOS experiment, which has been taking beam data since 2005. MINOS analyzes a neutrino beam in two different locations: at Fermilab, close to the beam production, and 735 km downstream in Northern Minnesota. By searching for neutrino disappearance as well as appearance, MINOS has been able to examine some of the neutrino mixing parameters that are a window into the new directions of physics. A brief history of neutrino physics and recent results since the discovery of oscillations will lead us to discuss the challenges of performing neutrino experiments. We will focus on how these challenges have been addressed in MINOS in obtaining the results from the first two years of beam data. We will aso briefly look into the future, when other experiments such as NOvA and LBNE will explore and unravel other pieces of the neutrino puzzle.
• December 9
  • Julie Kornfield, Caltech
  • Host: Ivan Smalyukh
  • Title: Flexible Chains in Nematic Solvents: Unimolecular Liquid Crystalline Gels?
  • Abstract: "Liquid" and "crystal" conjure images of "disorder" and "order" that play upon one another in the formation of liquid crystalline (LC) phases. These contradictory tendencies play a particularly pronounced role when a flexible chain polymer—which entropically favors a random coil conformation—is covalently linked to hundreds of mesogenic groups. Elastomers and gels made from such polymers exhibit dramatic changes of shape in response to temperature, light and electric fields. These are macroscopic manifestations of the distinctly non-random conformation of the backbone and its intimate coupling to the nematic order of the material as a whole. Here we examine the single-molecular analogue of LC gels: isolated polymers dissolved in a small molecule LC “host”. The chains do not disturb the director field, yet they exhibit long-range interactions when their host is in its nematic phase. When the host becomes isotropic, the tiny volume pervaded by a single chain can remain nematic, expelling some of the host to do so. Both the long-range interaction and the persistent nematic order can be explained by isolated coils perturbing—actually increasing—local order relative to the host alone. Far from having uniform order throughout the system, dilute solutions of SGLCPs exhibit heterogeneity. Each chain acts like an isolated “unimolecular gel” in equilibrium with the surrounding solvent, where the partitioning and local order of the LC solvent are dictated by the interplay between order and disorder inherent to each macromolecule.

Colloquia that have already occurred:

• August 26
  • Stuart Freedman, University of California, Berkeley and Lawrence Berkeley National Laboratory
  • Host: Ed Kinney
  • Title: Oscillating Neutrinos and Oscillating Decay Probabilities
  • Abstract: Recent experiments at the Gesellschaft fuer Schwerionenforschung (GSI) in Darmstadt claimed evidence for periodic modulation in the electron capture decay probability of hydrogen-like ions of 142Pm and 140Pr. These surprising observation have prompted suggestions that neutrino mass and neutrino mixing might cause such an effect. Experiments at Berkeley and Munich with electron capture in neutral atoms failed to confirm the GSI findings. I will review the positive and negative experimental evidence for modulation and some of the suggestions for the physics underlying the results. I will also discuss the state of the ongoing theoretical controversy about the compatibility of the neutrino explanation for the GSI effect with the basics principles of quantum mechanics.
• September 2
  • Sidney Nagel, University of Chicago
  • Host: Ivan Smalyukh
  • Title: The Life and Death of a Drop: Topological Transitions and Singularities in Fluids
  • Abstract: The exhilarating spray from waves crashing into the shore, the distressing sound of a faucet leaking in the night, and the indispensable role of bubbles dissolving gas into the oceans are but a few examples of the ubiquitous presence and profound importance of drop formation and splashing in our lives. They are also examples of a liquid changing its topology. Although part of our common everyday experience, these transitions are far from understood and reveal delightful and profound surprises upon careful investigation. For example in droplet fission, the fluid forms a neck that becomes vanishingly thin at the point of breakup. This topological transition is thus accompanied by a dynamic singularity in which physical properties such as pressure diverge. Singularities of this sort often organize the overall dynamical evolution of nonlinear systems. I will first discuss the role of singularities in the breakup of drops. I will then discuss the fate of the drop when it falls and eventually splashes against a solid surface and eventually evaporates.
• September 9
  • Meredith Betterton, University of Colorado
  • Host: Paul Beale
  • Title: Random walks, DNA elasticity, and the motion of proteins
  • Abstract: A particle undergoing a random walk is a classic physics problem that underlies our understanding of diffusion, the molecular nature of matter, polymer conformations, and the fluctuation-dissipation theorem. In addition to its conceptual importance in physics, a random walk is a surpisingly good model for some biophysical problems. This talk will present several examples, including DNA conformation and protein motion along a biopolymer, that are well described by a biased or unbiased random walk. I will discuss the physical theory and biophysical applications of several problems from our recent research: finite-length effects in DNA elasticity, the coupling of a biased walker with a fluctuating wall and traffic jams caused by crowding of multiple walkers.
• September 16
  • Victor Gurarie, University of Colorado
  • Host: Paul Beale
  • Title: Non-Abelian particles in a two dimensional world
  • Abstract: Non-Abelian particles are hypothetical quantum particles which are neither bosons nor fermions. They are presumed to live in some two dimensional many-body systems, although they were never observed in any experiment. They are also presumed, once they are observed, to provide the necessary breakthrough to build a working quantum computer. I will talk about what they are, where they can be found, and discuss various theoretical proposals to observe them in realistic condensed matter and cold atomic experiments.
• September 23
  • Hassan Jawahery, University of Maryland
  • Host: Jim Smith
  • Title: Matter-Antimatter Asymmetries: What Have We Learned at the B Factory Accelerators?
  • Abstract: Our universe appears to be matter dominated with no evidence for significant antimatter anywhere. However, it is an established fact, theoretically and experimentally, that for every known elementary particle there exists an antimatter counterpart, and the laws of nature are nearly symmetric with respect to matter and antimatter. The puzzle of the missing antimatter at the very large scale universe is believed to be connected to the differences in the behavior of matter and antimatter at the very small scale- the breaking of the CP symmetry that has been observed in the interactions and the decay of elementary particles. The B factory experiments were designed to explore the origin of the CP violation phenomenon: specifically to determine if the quark-mixing mechanism contained in the Standard Model of elementary particles and interactions is the source of the observed CP violation effects and the related matter antimatter asymmetries. In this talk, I will explain how the B factory experiments solved the puzzle- at least partially- a conclusion that led to the verification of the Standard Model mechanism for CP violation, now celebrated by the 2008 Nobel Prize in physics. I will also talk about the outlook for solving the rest of the puzzle.
• September 30
  • Juan Maldacena, Institute for Advanced Study
  • Host: Victor Gurarie
  • Title: QCD, strings and black holes: A duality between gravity and field theory
  • Abstract: The theory of strong interactions, QCD, has excitations that are well described by strings. These strings appear most simply in theories with a large number of colors, instead of the three colors we have in QCD. For theories that are similar in spirit to QCD one can relate these gauge theory strings to the strings of quantum gravity. In particular, some ten dimensional geometries are associated to four dimensional quantum field theories. We will describe how to use this relation to learn about strongly interacting quantum field theories. This duality also elucidates some puzzles regarding black holes.
• October 7
  • Mike Dubson, University of Colorado
  • Host: Steve Wagner
  • Title: An Airline Crash Investigation: Physics vs. Lawyers
  • Abstract: One hour before dawn, on July 26, 2002, FedEx flight 1478 crashed on landing at the Tallahassee Regional airport, one-half mile short of the runway. There was nothing wrong with the plane or the very experienced crew; visibility was 8 miles; the pilots could see the runway as they approached. Yet they flew into the ground. The crew of 3 survived, but were fired by FedEx because all those packages that were absolutely, positively guaranteed to be delivered the next day, burned up. The pilots contested their firing and presented their case before an Arbitration Board. I was hired by the Airline Pilots' Union to investigate the possibility that the crash was due to a failure of a runway lighting system called PAPI (Precision Approach Path Indicator). I was able to show experimentally that the PAPI very likely did fail due to condensation (dew) on the projection system. My conclusions directly contracted an earlier NTSB investigation and partially vindicated the pilots. Yet the pilots' lawyers decided that my testimony would not help their clients, and my results were not presented. I will present the physics and sociology of this curious case.
• October 14
  • Seth Fraden, Brandeis University
  • Host: Ivan Smalyukh
  • Title: Active Emulsions
  • Abstract: Many phenomena of biological importance involve synchronization of oscillatory components. We explore here, in several geometries, the behaviour of diffusively coupled, nanoliter volume, aqueous drops containing the reactants of the oscillatory Belousov-Zhabotinsky (BZ) reaction. A variety of synchronous regimes are found, including in- and anti-phase oscillations, stationary Turing patterns, and more complex combinations of stationary and oscillatory BZ-drops. A differential equation model based on a simplified description of the BZ chemistry and diffusion of messenger species reproduces a number of the experimental results. Biological applications and possibilities for a chemical computer are discussed.
• October 21
  • Shijie Zhong, University of Colorado
  • Host: Allan Franklin
  • Title: Supercontinent cycles, true polar wander, and very long-wavelength convection in the Earth's mantle
  • Abstract: This talk discusses the large-scale evolution of the Earth for the last 1 billion years, and possible physical mechanisms that control the evolution. The Earth's surface including seafloor and continents moves constantly at a slow rate in response to convective motions in the Earth's mantle. For the present-day Earth, while continents are scattered around on the surface, the convective structure within the mantle is predominated at a spherical harmonic degree 2. However, in the last 1 billion years, there are two episodes in which a supercontinent is formed as all the continents collide together and is later fragmented. Supercontinent formation and fragmentation are responsible for the most significant tectonic and volcanic events on the Earth. There is also evidence that the Earth may undergo a process of large-scale rigid body rotation, called true polar wander, during the supercontinent episodes. This talk will begin with an extensive review of relevant observations and inferences, and end with a physical mechanism of spherical harmonic degree-1 mantle convection to account for the diverse observations.
• October 28
  • Paul Romatschke, University of Washington
  • Host: Jamie Nagle
  • Title: Relativistic Viscous Fluid Dynamics: From Quarks to the Cosmos
  • Abstract: Quark soups, neutron stars, the cosmos and probably many other systems --- different as they may be --- have one thing in common: their bulk dynamics is aptly described by relativistic viscous fluid dynamics. This is possible because fluid dynamics is an effective theory of long wavelength perturbations, and as such is formally independent of system size, constituents, forces, etc. It may be the ultimate effective theory! I will review the modern formulation of relativistic viscous fluid dynamics and discuss some of its applications.
• November 4
  • Mark Stockman, Georgia State University
  • Host: Margaret Murnane
  • Title: Horizons of Nanoplasmonics: From Spaser to Attoseconds
  • Abstract: Nanoplasmonics deals with collective electron dynamics on the surface of metal nanostructures, which arises as a result of excitations called surface plasmons. The surface plasmons localize and concentrate optical energy in nanoscopic regions creating highly enhanced local optical fields. They undergo ultrafast dynamics with timescales as short as a few hundred attoseconds. We will review the numerous existing applications of nanoplasmonics: nanoantennas for photovoltaic cells and LEDs, nanoplasmonic labels, tests, and sensors for biology, medicine, industry, environmental monitoring and defense, ultramicroscopy, plasmonics-assisted magnetic recording, nanoshell-mediated cancer treatment, etc. From the latest developments and original work in nanoplasmonics, we will consider SPASER (quantum nanoscale optical generator and ultrafast amplifier) and attosecond nanoplasmonic field microscope.

Colloquium schedules from previous semesters can be found here

Contact: