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Spring 2004

Schedule Spring 2004

January 27, 2004
POSTPONED

Prof. John E. Thomas
Duke University

Experiments with a Strongly-interacting Degenerate Fermi Gas

Postponed until later this semester

Recent theory suggests that strongly interacting Fermi systems exhibit universal behavior. Hence, experiments which explore the dynamics of strongly interacting atomic Fermi gases provide measurements of parameters relevant to systems ranging from compact stellar objects to strongly correlated electrons. We use all-optical methods to produce a highly degenerate, two-component gas of fermionic 6-Li atoms at a temperature of 50 nK. An applied magnetic field (910 G) tunes the system to a collisional resonance where strong interactions are observed. This system provides an excellent starting point for studies of universal interactions and the onset of superfluidity at very high transition temperatures. I will describe measurements of novel expansion dynamics which may be a sign of superfluidity and measurements of the universal interaction energy which are in reasonable agreement with predictions for nuclear matter.


February 3, 2004
3:00 pm (Tuesday)

Prof. Don Madison
University of Missouri-Rolla

Why Would Anyone be Interested in Atomic Ionization by Charged Particle Impact?

In this talk, a general description of the problem of atomic ionization resulting from collisions with charged particles will be given with a particular emphasis on what can be learned from these types of studies. It will be demonstrated that, through a proper choice of dynamics, the method can be used to directly measure quantum mechanical wavefunctions, to investigate the details of collision dynamics or to directly examine the consequences of the Pauli principle. Examples of different types of collision will be given.


February 10, 2004
3:00 pm (Tuesday)

Dr. Rob S. Williamson
Alfalight, Inc.

The Physics of Telecommunications Devices

A broad overview of the architecture of an optical telecommunication network will be presented. A few key network elements (optoelectronic components) will be dissected, with emphasis on the optical physics and practical engineering considerations that go into each one. Components to be discussed in detail will include tunable lasers, optical modulators, high-speed receivers, and optical amplifiers. The talk will conclude with a brief commentary on the career transition from academic physicist to a commercial product development role.


March 2, 2004
3:00 pm (Tuesday)

Dr. James Bower
Research Imaging Center, University of Texas Health Center at San Antonio

Does the Olfactory System Detect Chemicals or Odors?

College of Sciences Dean's Distinguished Visitor Lecture Series

In 50 BC the Greek philosopher / scientist Lucretius postulated that agreeable odors were produced when the olfactory system encountered "smooth" particles, while disagreeable, harsh odors were generated by "hooked" particles. For the subsequent 2,000 years, the assumption that the olfactory system analyzes molecules based by attaching significance to general chemical characteristics (e.g. carbon chain investigations of olfaction. Based on an analysis of the descriptors used by humans to classify how molecules smell, we now suspect that classification in the olfactory system is not, in fact, organized along a metric of chemical characteristics. I will also present results obtained using computer simulations of olfactory receptor molecules that are consistent with this assertion. The results have important implications for studying the olfactory system at all levels.


March 3, 2004
7:00 pm (Wednesday)

Note unusual date and time

Dr. James Bower
Research Imaging Center - University of Texas Health Science Center at San Antonio

Whyville and Inquiry-Based Learning on the World Wide Web: A Town Hall Meeting

College of Sciences Dean's Distinguished Visitor Lecture Series

Whyville.net is an inquiry / constructivist virtual learning community that has attracted 700,000 registered users, average age 13 and 68% female. With an average log in of 60 minutes per user per visit, Whyville is also one of the stickiest sites on the Internet and was nominated for a Webby Award in 2003 as one of the five best sites for children on the World Wide Web. In this presentation, Dr. Bower, one of the site's four original founders, will discuss its history as well as the challenge of managing the learning and social experience of hundreds of thousands of pre and early teenage children. The presentation will also include a town hall meeting for Whyvillians living in and around Southern Virginia.


March 16, 2004
12:30 pm (Tuesday)

Dr. Steffen Strauch
George Washington University

Polarization measurements in single- and double-pion photoproduction on hydrogen

Please note unusual time and location

The nature of QCD confinement continues to provide an ongoing challenge to our understanding of soft QCD. Studying the baryon spectrum provides one avenue to learn more about this unique feature since the location and properties of excited states reflect the dynamics and relevant degrees-of-freedom within hadrons. Polarization measurements are for these studies an indispensable tool. I'll discuss such measurements in single- and double-pion photoproduction on hydrogen at Jefferson Lab.
Proton-recoil-polarization data in neutral-pion photoproduction exist from Hall A, and a single-pion photoproduction experiment with polarized beam and polarized hydrogen target using the CLAS detector got recently approved. The data will greatly constrain partial-wave analyses and reduce model-dependent uncertainties in the extraction of nucleon resonance properties.
I'll also present first results of a measurement of a new observable in double-charged-pion photoproduction on an unpolarized hydrogen target using the CLAS detector and a circularly polarized tagged photon beam. We have observed asymmetries in the beam-helicity-dependent angular distributions of the final-state particles as large as 40%, and these asymmetries show strong sensitivity to the kinematics of the reaction. Information on the reaction dynamics will be extracted from the data by means of model calculations. Calculations within a phenomenological model are currently underway. Comparisons of these model results with the experimental data at several kinematic settings will be shown.


March 16, 2004
3:00 pm (Tuesday)

Prof. R. Stephen Berry
University of Chicago, Chemistry Department

The Bizarre Phase Changes of Tiny Particles

College of Sciences Dean's Distinguished Visitor Lecture Series

Very small particles, from 5 or 10 to perhaps several million atoms or molecules, exhibit some properties very different from those of bulk matter. Some of the most striking are the phenomena associated with phase equilibria and changes of phase, e;g. of freezing and melting. Naive first impressions might make one think that such behavior, such as the coexistence of two (or more) phases over a band of temperatures and pressures, violates the laws of thermodynamics. In fact, the resolution of this paradox is not with any violation of thermodynamic laws but with the implicit constraints we apply when we use thermodynamics to describe ordinary bulk matter. We will examine the phase equilibria of small particles and see how this gives us new insights into the nature of phase changes of bulk matter, as well as of small particles.


March 17, 2004
7:00 pm (Wednesday)

Note unusual date and time

Prof. R. Stephen Berry
University of Chicago, Chemistry Department

Thermodynamics: Paradigm of the Mystery and Power of Science

College of Sciences Dean's Distinguished Visitor Lecture Series

Thermodynamics is one of the oldest sciences, and is probably the most universal, in its domain of applicability. It is remarkable in many ways. One is the very small number of variables one uses to describe systems of great complexity. But even more amazing is the capacity of the human mind to invent or discover those variables. Energy is perhaps the most striking, insofar as it encompasses such a range of apparently unrelated kinds of human experience. The development of the subject is a paradigm of a fundamental, basic science evolving from needs to solve very practical problems, a process virtually opposite to the direction we have been taught to expect. We shall examine the concepts on which thermodynamics rests, a little of how they evolved, and some of what we learn about nature by using these variables. For example, we shall see how thermodynamics sets limits on how well any process can perform, and how the subject offers new opportunities for potential exciting advances.


March 18, 2004
12:30 pm (Thursday)

Dr. Jeff Martin
CalTech

Strange Quarks in the Proton

Please note unusual time and location

The contribution of sea quarks to the everyday properties of the proton is of fundamental interest. A host of experiments are being conducted in order to address the question of how much of the proton's charge and magnetization are due to strange quarks. These experiments use the technique of parity-violating electron scattering in order to extract the strange quark contribution. In particular, I will focus on the G0 experiment (pronounced Gee-Zero) which has recently begun acquiring data in Hall C at Jefferson Lab.


March 25, 2004
12:30 pm (Thursday)

Note unusual date and time

Dr. Ioana Niculescu
James Madison University

Large Bjorken x: Convergence Point for High and Medium Energy Physics

Over the last thirty years or so nucleon structure functions have been measured over a wide range of x and Q2. However the region x>0.6, where a single quark carries most of the nucleon's momentum is not well explored. In this region contributions from quark-antiquark sea become negligible, and the structure functions are dominated by valence quarks. Measurements of structure functions at large x will yield insights into mechanisms responsible for spin-flavor symmetry breaking. In addition, quark distributions at large x are a crucial input for estimating backgrounds in searches for new physics beyond the Standard Model at high energy colliders. In this talk I will explore some of the ways in which this large-x region will be probed by experiments at Jefferson Lab and Fermilab.


March 30, 2004
12:30 pm (Tuesday)

Dr. Xiaochao Zheng
Argonne National Laboratory

Precision Measurements of the Neutron Spin Asymmetry in the Valence Quark Region

During experiment E99-117 in Hall A of Jefferson Lab, precision data were obtained, for the first time, on the neutron spin asymmetry A1n in the valence quark region. History of deep inelastic scattering (DIS) and the principle of using polarized DIS to study the nucleon spin structure will be reviewed. The experiment setup will be described. The final results will be presented and compared to various models, including the constituent quark model and the perturbative QCD. More example(s) on using spin observables to study the QCD and the hadron structure will be discussed.


March 30, 2004
POSTPONED

Prof. Lawrence B Weinstein
Old Dominion University

Title to be Announced

Postponed until next semester

During experiment E99-117 in Hall A of Jefferson Lab, precision data were obtained, for the first time, on the neutron spin asymmetry A1n in the valence quark region. History of deep inelastic scattering (DIS) and the principle of using polarized DIS to study the nucleon spin structure will be reviewed. The experiment setup will be described. The final results will be presented and compared to various models, including the constituent quark model and the perturbative QCD. More example(s) on using spin observables to study the QCD and the hadron structure will be discussed.


April 1, 2004
12:30 pm (Thursday)

Dr. Moskov Amarian
DESY

Prediction and Discovery of Pentaquarks

We will discuss theoretical predictions and postdictions for the existence of pentaquarks and review current status of experimental results. Experimental survey will include observation of Theta+ and Xi-- anti-strange pentaquarks as well as recently observed anti-charm pentaquark observed at HERA collider.


April 6, 2004
3:00 pm (Tuesday)

Prof. David M Ceperley
University of Illinois Urbana-Champaign

Path Integrals and Bose Condensation

In 1953 Feynman, introduced imaginary-time path integrals to understand superfluid 4He. Path integrals are an exact "isomorphism" between quantum systems and the classical statistical mechanics of ring "polymers" allowing one to understand Bose condensation from the point of view of classical statistical mechanics and to calculate rigorously many of its properties. Bose symmetry of the wave function implies that the polymers are allowed to ``cross-link'' or exchange. The specific heat singularity is a consequence of this cross-linking. Momentum condensation is related to the end-to-end distribution of a single open-ended polymer: if the ends become delocalized, the quantum system is bose condensed. Superfluidity (coupling to the boundaries) is proportional to the mean squared flux of polymers through a surface. We have developed specialized simulation methods (Path Integral Monte Carlo) based on the Metropolis Monte Carlo method, to simulate boson systems. We will discuss the application of these simulations to 4He droplets doped with impurities. Recent experiments have been able to probe superfluidity at a nanometer length scale in such droplets, verifying a prediction of the path integral simulations.

References: Ceperley, D. M., Path Integrals in the Theory of Condensed Helium , Rev. Mod. Phys. 67, 279 (1995).


April 13, 2004
3:00 pm (Tuesday)

Dr. Sergey O. Macheret
Department of Mechanical and Aerospace Engineering, Princeton University

Plasma Aerodynamics: Novel Technologies for High-Speed Flight

Weakly ionized gases (plasmas) can potentially revolutionize design and capabilities of supersonic and hypersonic vehicles. Plasmas can be used both as a means of heat delivery into the flow and as a way to manipulate the flow with electric and magnetic fields. The presentation discusses methods of highly efficient generation of "cold" plasmas. Electron beams and repetitive nanosecond pulses are shown to be capable of reducing the power budget for sustaining the plasmas by several orders of magnitude compared with more conventional methods. We then present results of theoretical and experimental studies of drag reduction and vehicle steering by plasma-controlled energy addition. Novel magnetohydrodynamic (MHD) devices, namely, those operating in cold hypersonic air flows ionized by electron beams, and applications of these devices for hypersonic airbreathing propulsion are then discussed. MHD devices are also shown to be attractive for power generation during atmospheric reentry and for aerodynamic control of reentry vehicles. We also discuss energy bypass concepts for hypersonic vehicles: energy generated by MHD is used to enhance the vehicle performance. Examples of the use of MHD-generated energy include: air capture increase in scramjet engines (the Virtual Cowl), energy addition for flow preconditioning and elimination of the isolator, and plasma-enhanced combustion.


April 20, 2004
3:00 pm (Tuesday)

Prof. David DeMille
Yale University

Fundamental physics with diatomic molecules: from CP violation to quantum computation

Our group is applying the techniques of precision measurement and quantum control that are common in atomic physics, to the more complex system of diatomic molecules. This is enabling unique types of leverage on a variety of problems of fundamental interest, ranging from tests of symmetry violations to the manipulation of complex many-body states of interest in condensed-matter physics. I will describe in detail two of our experiments. The first is a search for the CP-violating electric dipole moment of the electron, which is expected to reach an unprecedented level of sensitivity. The second centers around the production of ultracold polar molecules, with possible applications in large-scale quantum computing and other areas.


April 27, 2004
3:00 pm (Tuesday)

Dr. Joe Carlson
Los Alamos National Laboratory

Multiple Facets of Few-Nucleon Physics

Few-nucleon systems play multiple, diverse roles in physics. They were the first nuclei formed in the universe, and remain the dominant form of nuclei. Over the last several years experimental and theoretical studies of these nuclei have dramatically advanced our knowledge of their structure and dynamics. Theoretical calculations have confronted experimental data on nuclear spectra, charge and current distributions in the nucleus, and weak decays, for example. Our understanding has advanced to the point that these nuclei are now used as laboratories to study hadronic physics, including neutron form factors and hadronic parity violation. A survey of this physics, ranging from laboratory studies to astrophysical implications, will be presented.