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Fall 2004 Physics Colloquium ScheduleUnless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30. Abstracts are included below the schedule. The ORNL Physics Division Seminar Schedule might also be of interest. Professor Witek Nazarewicz is chair of the colloquium program. He may be contacted via e-mail at: witek@utk.edu. AbstractsAugust 23: Symmetry Violation, the Neutron, and the SNSGeoff Greene (UT Physics/ORNL) The study of the violation of fundamental symmetries such as parity and time reversal provides a powerful window into the details of particle physics, nuclear physics, and cosmology. Parity violation provides a unique signal by which the minute effects of the Weak Interaction can be identified in the presence of the nuclear Strongforce. Time reversal invariance violation can shed light on the very early phases of the Big Bang and may provide an explanation for the cosmic asymmetry between matter and antimatter. Precision measurements with low energy neutrons provide a very promising tool for such studies. Recent progress in the measurement of the neutron lifetime and the details of neutron decay as well as the search for a non-zero neutron electric dipole moment will be reviewed. The Fundamental Neutron Physics Beamline under construction at the SNS and the future program of research at UT and ORNL will be discussed.August 30: Exploring the Red PlanetHap McSween (UT Earth and Planetary Sciences) Two Mars Exploration Rovers (MERs) have been exploring sites on opposite sides of the planet for the past seven months. Spirit rover has taken thousands of images, analyzed rocks and soils, and driven 3.5 kilometers in Gusev Crater. Opportunity rover has similarly imaged and analyzed surface materials, and driven 1.5 kilometers in Meridiani Planum. Both rovers carry instrument packages designed to perform geologic characterization and especially to search for evidence of past water. Both missions (still operating) have succeeded beyond the wildest imagination of the NASA mission designers, in terms of engineering and scientific discoveries. Dr. McSween, as a MER Co-Investigator, will introduce the scientific findings of both rovers, as well as describe what it is like to participate in these spacecraft missions.September 13: The Cosmic Microwave Background: A New Window on Physics in the Early UniverseRobert Scherrer (Vanderbilt University) Beginning with the COBE mission in 1992, observations of the cosmic microwave background have yielded ever more precise measurements of its fluctuation spectrum, culminating in the recent data release from the Wilkinson Microwave Anisotropy Probe. Because this fluctuation spectrum depends on all of the important cosmological parameters, such as the matter density, the baryon density, and the Hubble parameter, a primary result of these observations is a set of sharp constraints on all of the important parameters in cosmology. However, the cosmic microwave background observations can also be used to place constraints on particle physics in the early universe. I will discuss several such constraints, including limits on neutrino (and other particle) masses and lifetimes, neutrino degeneracy, coupling between the dark matter and baryons, and time-variations in the fundamental constants.September 20: Synthetic Paths to the Heaviest ElementsWalter Loveland (Oregon State University) The heaviest elements provide a laboratory for studying nuclear structure and dynamics under the influence of large Coulomb forces. They offer opportunities for studying some of the most fundamental aspects of chemistry and physics. I review some of the recent developments in the chemistry of these elements. New results on the confirmation of the synthesis of element 110 (Ds) are reported along with new systematic studies of the synthesis of element 112 using hot fusion reactions. The story of the element 118 fiasco is told from an insider's perspective. New results on the survival probabilities of the heaviest elements (Z > = 102) from neutron counting and evaporation residue detection are discussed. The role of radioactive nuclear beams in future studies of the heaviest elements is discussed.September 27: Transition-Metal Oxides at the Nanoscales: a View from the BottomLia Krusin-Elbaum (IBM T.J. Watson Research Center) (CANCELLED) Self-organization offers nanotechnology a powerful alternative to standard nanofabrication approaches. Using self-assembly we have synthesized nanotubes of transition-metal oxides, such as VOx and RuOx, using monoamines as structure-directing templates. In this talk I will focus on the mixed-valent oxides of vanadium belonging to the class of strongly correlated systems which can host unusual quantum spin states, and exhibit a wide range of charge transport and optical behavior. I will describe our observation of a quantum frustrated spin-liquid (with a spin-gap Ds ~ 665 K) formed in `as-assembled' semiconducting nanotubes. This spin frustration succumbs to ferromagnetism upon electron or hole doping - a finding that offers an interesting path to new spin-aligned nanoscale building blocks. I will discuss how such magnetic particle-hole complementarity can arise from the low-dimensionality of the nanotube structure via crystal field splittings which enforce a Mott-Hubbard gap. The electron interactions in VOx can lead to a 1st order metal-insulator transition with an abrupt change in conductivity that can be as much as 11 orders of magnitude; at this transition there is also a sharp change in optical transmission in the infrared spectrum. Thus, numerous applications such as electrical, optical, and spin - temperature or voltage-controlled - switches can be envisioned.October 4: Out of Gas: The End of the Age of OilDavid Goodstein (Caltech) The world will start to run out of cheap, conventionally produced oil much sooner than most people expect, possibly within this decade. This talk will discuss the reasoning that leads to that conclusion and the likely consequences if it is correct. It may be possible, with considerable difficulty to substitute other fossil fuels for the missing oil, but if we do that we may do irreparable damage to Earth's climate. And even then we would start to run out of all fossil fuels, including coal, probably within this century. Can civilization survive if that happens? We will consider the possibilities.October 11: Neutron Scattering at the Frontier of Condensed Matter PhysicsStephen Nagler (ORNL) Most physicists in East Tennessee are aware that the Spallation Neutron Source will soon be the world's most powerful source of pulsed neutrons for neutron scattering research. At the same time, recent and ongoing upgrades to the facilities at the High Flux Isotope Reactor ensure that complementary world class capabilities for neutron scattering using continuous beams will exist at ORNL. This unique situation presents unparalleled opportunities for research in condensed matter physics as well as other areas of science. This talk will compare and contrast neutron scattering experiments at pulsed and continuous sources, illustrated by some real examples drawn primarily from research on quantum magnetism and highly correlated electron materials. Some of the exciting new instruments coming on board will be previewed, including the SEQUOIA chopper spectrometer at SNS and cold neutron instruments at HFIR.October 18: LIGO's Search for Gravitational WavesPeter R. Saulson (Syracuse University) The search for gravitational waves has entered a new era with the commissioning of the Laser Interferometer Gravitational Wave Observatory (LIGO) and its sister instruments around the world. The talk will review the nature and astrophysical signficance of gravitational waves, and give a brief overview of how they can be detected. Some early results of searches will be presented, along with the near- and medium-term prospects for the field of gravitational wave astronomy.October 25: Magnetic Nanostructures Beyond NatureJian Shen (ORNL Condensed Matter Sciences Division) The current standard of electronic devices and data storage media has reached a level such that magnetic materials have to be fabricated on a nanometer scale. In particular, the emerging concept of spintronics, which is based on fact that current carriers have not only charge but also spin, requires the assembling of nanometer-sized magnetic structures with desired magnetic properties. It is this background that motivates scientists and engineers to attempt to grow and characterize magnetic objects at smaller and smaller length scales, from 2D films and multilayers to 1D wires and eventually to 0D dots. In this talk, I will give a few examples to demonstrate how one can grow nanostructured magnetic materials including films, wires and dots by design. Some unexpected structural and magnetic properties of these materials will be discussed, with an emphasis on their physical origin. The emphasis is on converting the existing knowledge into growing and studying low-dimensional complex materials, which promise to have considerably higher ''tuning'' ability for desired properties.November 1: Complexity in Strongly Correlated Electronic SystemsElbio Dagotto (UT and ORNL) The area of Strongly Correlated Electrons is among the most active in condensed matter. A review of the main issues under discussion worldwide in the context of high temperature superconductors, colossal magnetoresistance manganites, and other transition metal oxides will be presented. Recent developments in the area of `complexity' in oxides will be addressed, with emphasis on the spontaneous formation of inhomogeneous states at the nanoscale.November 8: New CODATA Recommended Values of the Fundamental ConstantsPeter Mohr (NIST) The Committee on Data for Science and Technology (CODATA) has recently recommended a new self-consistent set of values of basic constants and conversion factors of physics and chemistry. The values are based on a least-squares analysis that takes into account all of the latest relevant experimental and theoretical information in a consistent framework. This analysis and the new information that has influenced the values of the constants will be described.November 15: Neutrinos: The Mass that RoaredR.G. Hamish Robertson (Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington) Physicists have grown up thinking of the "electron neutrino" as a neutral elementary particle that accompanies beta decay, streams from the sun as it produces its energy, and fills the universe as a primordial relic. It has thus been somewhat of a shock to find experimentally that it is not a particle at all, but a quantum-mechanical superposition of three different massive particles that each have a mixture of flavors. The masses, tiny though they are, have exposed this master of disguise for what it is, and in the process have revealed the first flaw in the trusty Standard Model. We will summarize where we stand, report new results on solar neutrinos from the Sudbury Neutrino Observatory, and speculate on where all this might be headed.November 22: How much does a Neutrino Weigh? Measuring the Smallest Mass in the UniverseGiorgio Gratta (Stanford University) With the definite evidence for neutrino oscillations collected in the
last few years we now believe that neutrino masses are non-zero. Oscillation
measurements, however, only measure mass differences and give us little
information about the absolute values of neutrino masses.
November 29: Probing Novel Superconductors through PhotoelectronsHong Ding (Boston College) Angle-resolved photoelectron spectroscopy (AREPS) has become a powerful technique in probing electronic structures of quasi two-dimensional novel superconductors due to its unique capability of “seeing” single-particle excitations in a solid. I will review some important results from ARPES on the high temperature superconductors and some new superconducting materials, including measurements of Fermi surface, superconducting gap, pseudogap, and many-body interactions. Previous Physics Department Colloquia: |
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