Full Abstracts

 September 9, 2009

 Philip Argyres, University of Cincinnati

"Quark-Gluon Plasma and Strings"
I explain how techniques from string theory shed light on recent experimental results from high energy heavy ion collisions.  A surprising equivalence between strongly-coupled quantum gauge theory systems and certain higher-dimensional classical gravitational systems is a result of the string theory description of quantum gravity.  This equivalence allows some difficult problems concerning the strong nuclear force to be recast as easier ones invloving the classical dynamics of objects in the presence of black holes.

October 7, 2009

Stephen E. Nagler, Oak Ridge National Laboratory
"Magnetism and Superconductivity in the Iron Age"
Since early 2008 there has been great excitement and much research effort directed towards understanding a new class of superconducting materials, the co-called “iron based superconductors”. These are characterized by the presence of a square lattice of iron atoms, each in a tetrahedrally co-ordinated local environment, and are closely related to magnetically ordered parent compounds. In this talk I will briefly review some recent history of research on these materials, followed by a discussion of neutron scattering measurements of the magnetic structure and excitations. The last part of the talk will focus on recent studies of the “resonant” magnetic excitation and in particular inelastic neutron scattering experiments on single crystals.

 October 14, 2009

Scott Nutter, Northern Kentucky University
"Indirect Dark Matter Search: Measurements of Cosmic-Ray Positrons, Electrons & Antiprotons"
Recent measurements of cosmic ray (CR) positrons and electrons by the PAMELA and ATIC experiments have generated much excitement.  The measurements have been variously interpreted as indications of dark matter (DM).  Of course, other interpretations, such as astrophysical sources, are possible, but the DM interpretations have garnered much more discussion.  It is important to note that these instruments were designed to measure CR spectra, and a search for DM signatures is not the primary motivation for either experiment. The current results also should be understood within the historical context of earlier CR antimatter measurements, and other more recent measurements, such as the HEAT and FERMI results.  This talk will give an particle astrophysics experimentalist's perspective on what to make of these sometimes conflicting results.

October 21, 2009

Leo Irakliotis, University of Chicago

"The Turk and the Mainframe: A Physicist's Retro(per)spective"
The Turk was a chess playing automaton that appeared in the 19th century.  For more than half a century the Turk tricked people in believing that it possessed what we'd call today artificial intelligence.  As the automaton toured Europe, it inspired a young Cambridge mathematician to develop a mechanical computing device which, in turn, inspired a young lady to write "programs" for that device.  Since the time of Charles Babbage and Ada Lovelace, computing has grown by leaps and bounds to become our time's principal platform for productivity, creativity, and discovery.  In the past 30 years I have programmed computers that helped me learn and discover things; I have designed and built super-fast machines; and I have applied computational techniques to help fight crime in Chicago.  I will discuss some of this work along with new emerging ideas that are keeping me busy these days: including the overall efficiency of human-computer interfaces, neuroscience, and education.  Emphasis will be given on the enduring (and endearing) value of physics as a foundational discipline that has helped at least one aspiring academic (yours truly) to stay -- mostly -- out of trouble.   

October 28, 2009

Paul Stankus, Oak Ridge National Laboratory

"Hot Gold: Life at a Trillion Degrees"
What happens to matter at very high temperatures?  Its properties at millions or even billions of degrees are fairly well-known; but at a trillion degrees things start to get really interesting.  We review the basic descriptions of high-temperature matter, including the concept of a "maximum limiting temperature."  We then discuss how trillion-degree matter is currently being created and diagnosed in the laboratory, and some surprising results about its properties.

  November 4, 2009

Julio Gea-Banacloche, University of Arkansas

"Energy constraints for quantum computation"
Quantum information processing has been a "hot" research topic for over a decade, but how much energy does it take to do the processing?  A number of results obtained in recent years indicate that, when the quantum nature of the control systems is taken into account, the minimum energy required to carry out a "quantum logic" operation is inversely proportional to the tolerable error rate.  Ascertaining the full generality of this result remains an ongoing challenge.
 

November 5, 2009

Julio Gea-Banacloche, University of Arkansas, Public Lecture

"Fate and Physicists"

Do we live in a universe whose future is—to some extent, at least—open?  Or is everything that is to happen already predetermined?  Throughout human history, philosophers have struggled with the question, writers have played with it for dramatic effect, and scientists, especially physicists, have occasionally claimed to know the answer.  This talk will review some of the history of the problem and explain our current understanding of what may be called the “creative freedom” of the physical world.

December 2, 2009

Herb Fertig, Indiana University

"Graphene: A New Two-Dimensional Electron System"
Recent experimental advances have led to the laboratory realization of graphene, a two-dimensional honeycomb network of carbon atoms that forms the building block of graphite, carbon nanotubes, and buckeyballs.  This development has created tremendous excitement both for proposed applications in devices, and for the very unusual fundamental electron physics that it supports at low energies.  Remarkably, the latter is a {\it massless} electron theory, reminiscent of simple models for neutrinos.  In the first part of the talk I will outline some of the developments that have generated so much interest, both in zero and finite magnetic fields.

One of the remarkable properties of this system is how it behaves in a magnetic field.  Experiments show either metallic or insulating behavior, depending on sample quality and strength of magnetic field, and strong signs of a quantum phase transition separating the two regimes.  I will discuss how such behavior can emerge naturally due physics at the edge of the system, and show that the metallic behavior can be interpreted in terms of a superconducting gap in an otherwise insulating one-dimensional system.

December 9, 2009

Shiou-Jyh Hwu, Clemson University

"New Extended Solids Containing Quantized Magnetic Nanostructures"
Quantum spin systems, such as spin-Peierls, spin-dimers, and geometrically frustrated ladder compounds, have drawn considerable attention due to their theoretical and experimental importance. These solids, mostly composed of transition-metal oxides and halides, are known as magnetic insulators due to the discrete nature of the magnetic nanostructures found within these otherwise extended frameworks. Despite the simplicity of their low-dimensional structural features, these compounds show effects of strong electronic correlations and magnetism induced by the interplay between spin, charge and orbital degrees of freedom. It has been realized that compounds of this type can be model systems that provide insight into electronic mechanisms that give rise to complex physical phenomena, such as high-temperature superconductivity. Some recent findings, demonstrating exotic magnetic behaviors relevant to quantum spin relaxation, bring new excitement to this rapidly growing field of technological significance.

A new class of extended solids containing quantized magnetic nanostructures has been systematically explored in the A-M-X-O quaternary systems (where A = mono- and divalent electropositive cations, M = transition metal (TM) cations, and X = Si, P, As). A large collection of new compounds, exhibiting fascinating structural chemistry due to the versatility of the mixed-framework structures made of MOn (n = 4~6) and XO4 polyhedra, has been isolated. The XO4 oxyanions, because of their closed-shell, nonmagnetic nature, are employed to facilitate structural isolation and electronic confinement of magnetic nanostructures of fused MOn polyhedra. These solids also exhibit rich magnetochemistry dependent upon the geometry, size, and shape of the corresponding magnetic nanostructures, such as stepped variations in magnetic-field-driven magnetization. These magnetic compounds offer new opportunities to study quantum effects in a class of pseudo-low-dimensional materials complementary to the traditional molecular-based systems. In this seminar, exploratory synthesis, structure, and properties of these new solids will be presented. The variations of magnetochemistry will also be discussed in terms of the size and geometry of the magnetic nanostructures.

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