Fall 2005 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. Abstracts are included below the schedule. The ORNL Physics Division Seminar Schedule might also be of interest. Professor John Quinn is chair of the colloquium program. He may be contacted via e-mail at: jjquinn@utk.edu.

Abstracts

August 29

Dr. Richard Thomas, Stockholm University

The Fragmentation of Molecular Ions following Electron Attachment: Dissociative Recombination from Interstellar Clouds to Planetary Atmospheres and Combustion

Plasma environments that contain molecules cover many orders of magnitude in size, temperature, and complexity, ranging from diffuse interstellar clouds and planetary atmospheres down to combustion engines and semiconductor etching. The physical and chemical evolution of these environments is dictated by many internal and external factors and one of the most fundamental and explosive processes occurs when a molecular ion attaches a low-energy electron and fragments into neutral products, dissociative recombination. This reaction has varied and far reaching effects, from the observed isotope fractionation in the Martian atmosphere and the skyglow in Earth's, to the production of fundamental molecules in interstellar clouds and more efficient combustion engines. To understand these environments enough to create complete and predictive models, detailed knowledge of these reactions on a macroscopic and quantum level is required to couple with observation and intuition.

September 19

Dr. Alexios Polychronakos, City College (CUNY)

Turning Fermions into Bosons

Bosonization, the description of a system of fermions in terms of bosonic degrees of freedom, has been a standard technique in the condensed matter physics of one-dimensional systems for the last three decades. Its exportation to higher spatial dimensions, however, is still a largely open question. In an approach deriving from the exotic notion of noncommutative geometry, arising in string and field theory, the bosonization of higher dimensional fermi systems is achieved in terms of a "fuzzy phase space fluid". The collective properties of such systems can thus be derived using bosonic techniques.

September 26

Dr. Jim Cline, McGill University

Inflation from String Theory

I discuss recent progress in obtaining inflation in the early universe using elements of string theory, especially the annihilation of branes with antibranes. After reviewing essential elements of inflation and string theory, I will show how these can be combined to provide possible tests of string theory using observations of the cosmic microwave background and large scale structure of the universe.

October 3

Dr. Anders Nilsson, Stanford Synchrotron Radiation Laboratory, Stanford University

The Structure of Liquid Water

In many processes in technology and nature, hydrogen bonding (H-bonding) is involved as an essential component. The H-bond in liquid water holds the key to its peculiar behavior, with implications for chemical, biological and geological processes. In the present talk I will show how we can address the nature of the H-bond and its connection to the structure of liquid water using a combination of X-ray spectroscopy and Density Functional Theory (DFT) calculations. X-ray Absorption Spectroscopy (XAS), X-ray Emission Spectroscopy (XES) and X-ray Raman Scattering (XRS) provides direct information on how occupied and unoccupied orbitals locally around the oxygen atom are transformed upon condensation of water to form ice, ambient water, supercritical water and water adsorbed on surfaces. In particular the recent result on the structure of the first coordination shell in liquid water (1) challenges many current models based on molecular dynamic simulations.

1. Wernet et. al. , Science 304, 995 (2004).

October 10

Dr. Allan MacDonald, The University of Texas, Austin

Anomalous Transport

In ferromagnetic metals and semiconductors the Hall effect has an unusual contribution due to coherence between Bloch bands induced by an external electric field. A similar transverse current of spins occurs in paramagnetic metals and contributes to the spin Hall effect. We refer to these transport effects as anomalous transport. When disorder is neglected, the anomalous Hall transport of a ferromagnet is dependent only on Berry phases associated with the variation of Bloch states with wavevector in momentum space. I will discuss the physics which determines the size of the Berry phase Hall and spin Hall conductivities in various systems, including transition metal and diluted magnetic semiconductor ferromagnets.

October 24

Dr. David Dean, ORNL Physics Division and UT Department of Physics and Astronomy

Simplicity and Complexity in the Study of Nuclei

Investigations of rare isotopes in the laboratory will open the way to understand and clarify the properties of all nuclei and bulk nuclear matter. In this talk I will assess where we stand today in solving the nuclear problem and how future rare isotope facilities will impact our understanding of nuclei. The first part of the nuclear problem concerns our ability to describe complex nuclei from the ground up using as input the basic interactions among protons and neutrons. We are on the verge of discovering how light nuclear systems are built from bare nuclear interactions that have their roots in QCD. I will describe this exciting frontier of research through illustrating recent progress in the nuclear implementation of coupled-cluster methods, a quantum many-body technique enjoying great success in quantum chemistry. A second and equally amazing aspect of the nuclear problem involves the occurrence of many-body phenomena such as the development of shell structure, collective excitations, pairing super-fluidity, and deformation, many of which are also found in other quantum many-body systems. I will describe the interplay between nuclear pairing and deformation as a function of increasing excitation energy in mass 60-80 nuclei (from neutron-rich to neutron deficient) where a wealth of rich and varied many-body phenomena exits. Studies of nuclei in the framework of quantum many-body theory require significant computational capability; I will also briefly touch on this theme and its importance to the future of nuclear theory research.

October 31

Dr. Robert Compton, UT Departments of Chemistry and Physics

Multiple-Bound Molecular Anions

Recent experimental and theoretical studies in the field of negative ion physics have shown that in some cases it is useful to describe the binding of an electron to a molecule as a result of the dominant multipole moment of that molecule (e.g., dipole, quadrupole, etc.) together with the polarizability attraction. These anions are exceedingly weakly bound and are subject to collisional detachment as well as detachment by modest electric fields or low-energy photons. A plot of the electron affinities for over fifty dipole-bound anions shows a minimum dipole moment of ~ 2.5 Debye to bind an excess electron. This agrees with general theoretical estimates of the “minimum” dipole moment required to bind an electron to a polar molecule. Recently, we have shown that the succinonitrile molecule can support both a dipole-bound anion in its gauche form (EA ~ 108 meV) and a quadrupole-bound anion in its trans form (EA ~ 20 meV)[PRL, 92, 83003].
The concept of electron-molecule multipole expansion is especially useful in the description of multiply-charged negative ions. The combined monopole (Coulomb repulsion) and polarizability attraction of an electron with a molecular negative ion gives rise to a “Coulomb barrier” for the addition or removal of the extra electron. This simple picture qualitatively explains many of the prominent features of multiply-charged anions. The majority of this talk will discuss recent studies on the formation mechanisms and subsequent collision induced dissociation of multiply-charged anions.

November 14

Dr. Thomas Weiler, Vanderbilt University

Mysteries and Opportunities with CosmicRay/Neutrino Astrophysics

Arguably the most pressing mysteries in extreme-energy cosmic-ray physics are the unknown sources of the particles, and the unknown maximum energy of the spectrum. Data from AGASA in Japan, HiRes in Utah, and most recently Auger in Argentina will be reviewed; source models, and controversies, will be discussed. A major advance will soon be made with "neutrino telescopes"; we present examples where cosmic neutrino measurements can elucidate issues in astrophysics and particle physics.

Previous Physics Department Colloquia:

• Fall 2005
• Spring 2005
• Fall 2004
• Spring 2004
• Fall 2003
• Spring 2003
• Fall 2002