Fall 2009 Physics Colloquium Schedule
Unless 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. The ORNL Physics Division Seminar Schedule might also be of interest. Professor Ken Read is chair of the colloquium program. He may be contacted via e-mail at: readkf@ornl.gov.
Physics Colloquium Webcasts
| Date | Speaker and Title |
|---|---|
| August 24 | Geoff Greene, UT Physics/ORNL “Nuclear and particle physics at the Spallation Neutron Source” |
| August 31 | Jaewook Joo, UT Physics/NIOMBioS "Mathematical challenges in theoretical biology: networks, dynamics, and noise" |
| September 7 | Labor Day Holiday |
| September 14 | Achim Schwenk, TRIUMF “A tour of neutron-rich matter in the universe” |
| September 21 | Alex Wolszczan, Pennsylvania State University "Planets around evolved stars" |
| September 28 | Bruce Gaulin, McMaster University "Frustrated and satisfied ground states in pyrochlore magnets" |
| October 5 | CANCELLED Richard Hughes, LANL "Twenty-five years of quantum key distribution" |
| October 12 | Alexei Sokolov, UT-ORNL Governor's Chair "Glass transition and its relevance to biological systems" |
| October 19 | CANCELLED James Hack, Director of NCCS, ORNL “Scientific and computational challenges for climate change research” |
| October 26 | Stuart Raby, Ohio State University "The Puzzle of Charge and Mass" |
| November 2 | Joan Centrella, NASA Goddard Space Flight Center "Merging black holes" |
| November 9 | Dan McKinsey, Yale University “Direct searches for dark matter particles” |
| November 16 | Vidya Madhavan, Boston College “STM studies of correlated electron systems” |
| November 23 | John W. Harris, Yale University “Recreating the Primordial Quark-Gluon Soup” |
| November 30 | Jeremy Smith, UT-ORNL Governor’s Chair “The physics of biomolecules” |
Abstracts
August 31
Jaewook Joo, UT Physics/NIMBioS
"Mathematical challenges in theoretical biology: networks, dynamics, and noise"
A key aim of postgenomic biomedical research is to systematically understand the structure and the dynamics of the complex intercellular web of interactions between proteins, DNA, RNA, and small molecules that contribute to the function of a living cell. Such a network of interactions is a dynamic system evolving in time and space according to fundamental laws of reaction, diffusion and transport. These laws govern how a biological network, confronted by any set of stimuli, determines the appropriate response of a cell. This information processing system can be described in precise mathematical terms and the resulting equations can be analyzed and simulated to provide reliable, testable accounts of the molecular control of cell behavior. In this talk, I will discuss the mathematical challenges in understanding the dynamics of the complex biological networks and especially will focus on the effect of noise on such a dynamical system.
August 24
Geoff Greene, UT Physics/ORNL
"Nuclear and particle physics at the Spallation Neutron Source"
As it ramps up to full power, the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is the most intense pulsed neutron source in the world. While the focus of research at the SNS concerns neutron scattering studies in materials science and condensed matter research, the SNS scientific program extends to nuclear and particle physics and one beamline has been devoted to these studies. This “Fundamental Neutron Physics Beamline” (FNPB) will address questions in weak interaction physics, symmetry violation and cosmology using extremely low energy (“cold” and “ultracold”) neutrons. The talk will give a general introduction to the SNS facility and a very brief discussion of neutron scattering. The first two approved experiments at the FNPB involving Hadronic parity violation and the neutron electric dipole moment will be reviewed in some detail. A summary of other possible experiments will be given.
September 14
Achim Schwenk, TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics
"A tour of neutron-rich matter in the universe"
I will take you on a tour of the physics of neutrons in the universe. The tour leads us through astrophysics, atomic, nuclear and particle physics and highlights:
- the physics of strong interactions between neutrons,
- universal properties of neutrons and ultracold atoms,
- neutron superfluidity in neutron stars,
- novel forms of matter and the limits of existence of neutron-rich nuclei, and
- how neutrinos interact with neutrons in supernovae.
September 21
Alex Wolszczan, Penn State University Center for Exoplanets and Habitable Worlds
"Planets around evolved stars"
Discoveries of planets around Sun-like stars have taught us much about the nature of extrasolar planetary systems. However, issues such as planet formation around higher mass stars and long-term evolution of planetary systems have been left out from the mainstream exoplanet research, because the radial velocity method of planet detection becomes inefficient for spectral types earlier than F6-F8. An attractive way to remove this deficiency is to search for planets around giant stars, which have cool atmospheres and their spectra are rich in absorption lines that can be used for planet detection.
In addition, planets have been discovered around neutron stars, a post-red-giant star and, possibly, around at least one white dwarf, all of which demonstrates the spectacular robustness of the planet formation process. In this talk, I will review the development of this relatively new field in the exoplanet research and present the Penn State - Torun Centre for Astronomy search for planets around GK-giants and other stars with the 9.2-m Hobby-Eberly Telescope.
September 28
Bruce Gaulin, McMaster University
"Frustrated and satisfied ground states in pyrochlore magnets"
Geometrical frustration arises quite generally when pairwise interactions in magnetic materials are incompatable with their local geometry. This often involves magnetic materials made up of assemblies of triangles or tetrahedra. The frustration is manifest by disordered low temperature states for the magnetic material - some of which are described by spin liquids, spin glasses, and spin ice. I will discuss (mostly) neutron scattering work on two magnetic pyrochlores Tb2Ti2O7 and Ho2Ti2O7, which can be thought of as Ising-like moments decorating a network of corner-sharing tetrahedra. Tb2Ti2O7 displays a spin liquid, or cooperative paramagnetic ground state, but can be brought to order in an applied magnetic field. Ho2Ti2O7 displays a static disordered "spin ice" state at low temperatures.
October 12
Alexei P. Sokolov, UT/ORNL Governor’s Chair
"Glass transition and its relevance to biological systems"
For thousands of years people are using glass transition process and glasses in their everyday life. For hundreds of years researchers are studying the glass transition phenomenon. However, understanding the microscopic mechanism underlying the tremendous slowing down of structural relaxation remains one of the main challenges in current condensed matter physics.
This talk will present an overview of new ideas and experimental results generated in this field during the last two decades. It appears that the glass transition on a molecular level occurs at temperatures much above the conventional glass transition temperature. Understanding of this important point shifted significantly the focus of the current research and resulted in deeper microscopic understanding of the glass transition. In a recent decade it has been realized that the glass transition is actively used in nature. In particular, living organisms use the glass transition to survive in extreme environmental conditions. A role of the glass transition in biology and in preservation of biological molecules and organisms will be discussed at the end of the talk.
October 26
Stuart Raby, Ohio State University
"The Puzzle of Charge and Mass"
Beginning with the seminal work of Rutherford, Geiger and Marsden in 1911, physicists have investigated the atom using particle beams (alpha particles, and protons) as probes. They developed new detection methods; the geiger counter, scintillators, cloud and then bubble chambers. This new paradigm for probing matter and new detectors led to many discoveries.
To make a long story short, by 1974 the chaos of discovery lead to the Standard Model describing all observed particle phenomena in terms of three fundamental forces (4 including gravity) and the fundamental building blocks of matter, quarks and leptons.
Only now, after the dust of this chaotic discovery settles, are we able with hindsight to recognize the underlying principles which define the theory we call the Standard Model. It is these principles and their logical extension which I will attempt to describe in this talk.
November 2
Joan Centrella, NASA Goddard Space Flight Center
"Merging black holes"
The final merger of two black holes is expected to be the strongest source of gravitational waves for both ground-based detectors such as LIGO and VIRGO, as well as the space-based LISA. Since the merger takes place in the regime of strong dynamical gravity, computing the resulting gravitational waveforms requires solving the full Einstein equations of general relativity on a computer. For many years, numerical codes designed to simulate black hole mergers were plagued by a host of instabilities. However, recent breakthroughs have conquered these instabilities and opened up this field dramatically. This talk will focus on the resulting gold rush of new results that are revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, testing general relativity, and astrophysics.
November 9
Dan McKinsey, Yale University
"Direct searches for dark matter particles"
Astrophysical evidence on a variety of distance scales clearly shows that we cannot account for a large fraction of the mass of the universe. This matter is “dark,” not emitting or absorbing any electromagnetic radiation. A compelling explanation for this missing mass is the existence of Weakly Interacting Massive Particles (WIMPs).
These particles are well motivated by particle physics theories beyond the Standard Model, and the discovery of WIMPs would have enormous impact on both astrophysics and particle physics. WIMPs, if they exist, would occasionally interact with normal matter. With a mass in the range of 1 to 1000 times the mass of the proton, and moving at speeds relative to the Earth of about 220 km/s (the velocity of the Sun around the MilkyWay), WIMPs would only deposit a small amount of energy when scattering with nuclei.
Detectors that are low in radioactivity and sensitive to small energy depositions can search for the rare nuclear recoil events predicted by WIMP models. One experiment, known as DAMA, claims a dark matter signal based on an observed annual modulation of the event rate in sodium iodide crystals. In recent years, several new efforts on direct dark matter detection have begun in which the detection material is a noble liquid. Advantages include: large nuclear recoil signals in both scintillation and ionization channels, good scalability to large target masses, effective discrimination against gamma ray backgrounds, easy purification, and reasonable cost.
November 16
Vidya Madhavan, Boston College
"STM studies of correlated electron systems"
Correlated electron systems often exhibit emergent behavior and manifest unexpected properties that cannot be understood in within a single electron picture. Over the last few decades, many new theoretical and experimental techniques have been developed to further our understanding of these intriguing materials. Scanning Tunneling Microscopy (STM) and spectroscopy (STS) have emerged as powerful tools in this context. In astonishingly successful series of experiments, STM studies of high temperature superconductors have contributed critical information to advance our understanding of these correlated materials at the nanoscale. In this talk I will explore two distinct high temperature superconductors: cuprates and the newly discovered pnictides. I will begin with a general discussion of these materials and what we have learnt from STM. I will end with a recent STM experiment where imaging and spectroscopic mapping allowed us to solve a puzzle involving the nature of the surface of the pnictides.
November 23
John W. Harris, Yale University
"Recreating the Primordial Quark-Gluon Soup"
Ultra-relativistic collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC), and soon at the Large Hadron Collider (LHC), create a system at temperatures (T) typically expected only within the first microseconds after the Big Bang. Here at T ~ 1012K, normal hadrons cannot exist and nuclear matter “melts” to form a soup of deconfined quarks and gluons. At RHIC, the soup flows with extremely low viscosity, suggesting a nearly perfect hot liquid of quarks and gluons. Furthermore, the liquid is opaque to very energetic quark and gluon probes (partons) providing evidence that it is dense and strongly-coupled. I will present a brief motivation for physics in the field, an overview and interpretation of the RHIC results, and a perspective on future fascinating results that are anticipated with heavy ions at the LHC.