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Fall 2002

Schedule Fall 2002

September 12, 2002
4:30 pm (Thursday)

Prof. Jim H. McGuire
Tulane University

Correlation in space and time in dynamic multi-particle systems.

Correlation in a key to complexity in many body systems. It is especially evident in few particle transitions in both atomic and nuclear reactions. We give an overview of conventional "mechanisms for dynamic correlation" in the spatial regime. We also define correlation in time between particles. Correlation in time is compared to correlation in space. Some recent experiments are discussed.

September 26, 2002
4:30 pm (Thursday)

Dr. Nicolas C. Pyper
University Chemical Laboratories, University of Cambridge

Helium bubbles in metals and the lowest allowed electronic transition.

October 4, 2002
3:00 pm (Friday)

Note unusual date and time

Prof. David M. Van Wie
Johns Hopkins University, Applied Physics Laboratory

MHD Control of Scramjet Inlets

Magnetohydrodynamic (MHD) control of scramjet inlets offers the potential for improving the operating characteristics of hypersonic inlets that must over a wide Mach number range. Significant technological hurdles that must be overcome in the development of MHD control include non-equilibrium ionization of the airstream, generation of a uniform magnetic field using a light weight magnet system, minimization of Joule heating, and effective coupling of the MHD control system without destroying basic inlet operating characteristics. Combined experimental and computational efforts are now underway to understand the physical processes associated with MHD inlet flow control. This presentation will focus on recent experimental results conducted in collaboration with the Ioffe Physico-Technical Institute dealing with the non-equilibrium flow of rare-gas plasmas through an MHD controlled inlet. Results demonstrating a significant level of MHD flow control will be provided together with an assessment of major remaining challenges.

October 10, 2002
4:30 pm (Thursday)

Dr. Skip Williams
Air Force Research Laboratory

Gas Phase Ion-Molecule Reactions Relevant to Plasma-Assisted Combustion

The effects of ionization on hydrocarbon-air combustion chemistry are being investigated for the purpose of developing techniques to reduce the ignition delay time and increase the rate of combustion of hydrocarbon fuels. The investigations focus primarily on the development of plasma-based ignition and combustion/mixing enhancement for scramjet engines. However, the methods pursued are based on detailed fundamental kinetics treatments and are therefore broadly applicable to a wide range of problems such as combustors for gas turbine engines, spark inhibition, improved engine performance, service life, explosion limits in blended fuels, hydrocarbon molecular growth, and high altitude relight. In the present contribution, the kinetics of reactions between air plasma ions with C7-C9 linear and cyclic alkane and alkylbenzene species typically found in aviation (JP) fuels are studied over 300 - 1300 K using fast ion flow tube techniques. The oxidation mechanisms of a select number of secondary hydrocarbon ions formed in these reactions are also presented. The new
measurements are presented in the context of previous work when available, and the implications for detailed kinetic modeling applications are discussed.

October 24, 2002
4:30 pm (Thursday)

Prof. Charles E. Hyde-Wright
Old Dominion University

The Squishiness of the Proton

Rather than an atom smasher, Jefferson Lab is a tool for very gently shaking the atomic nucleus. In the Virtual Compton Scattering process, we select events where a high energy electron in the beam scatters off of a proton in the liquid hydrogen target, and the
recoiling, vibrating, proton shakes off a gamma-ray. In this process, we observe the deformation of the internal structure of the proton, as it is stressed by electric and magnetic forces.

October 31, 2002
4:30 pm (Thursday)

Prof. R. Jeffrey Balla
NASA Langley Research Center

Laser-Induced Thermal Acoustics (LITA) : Theory and Fluid Dynamics

To advance our understanding of fluid mechanics, new optical instrumentation is required capable of 1% accurate measurements. Laser-Induced Thermal Acoustics (LITA) is a promising new nonlinear optical technique capable of meeting this challenge. In LITA a short-pulse (10 ns) driver laser is split into two beams which are crossed at a small angle
typically 1 degree and focused. Interference of the beams near the focal point creates an optical-electric-field intensity grating. This grating via opto-acoustic effects (electrostriction) launches two counterpropragating acoustic waves. Light from a continuous wave laser scatters off the acoustic waves and forms a coherent signal beam whose time history is
recorded. Bulk fluid properties are obtained by fitting the waveform to an appropriate model. LITA non-intrusively measures speed of sound of a fluid from which temperature is computed. Heterodyne detection of LITA signals also provides one component of the fluid velocity via the Doppler shift of the signal beam. We have demonstrated measurements of speed of sound(0.1%), temperature(1%), and velocity(+- 1m/sec) in room air with listed uncertainties. Experimental results on a rearward facing step model in the Basic Aerodynamics Research Tunnel(BART) will also be presented.

November 7, 2002
4:30 pm (Thursday)

Prof. Richard Miles
Mechanical and Aerospace Engineering, Princeton University

Breaking the limits of hypersonic testing and vehicle design with electron beams

Using electron beams to deposit energy into a high speed flow and to control conductivity of low temperature air open up new possibilities for the development of hypersonic vehicles. All aircraft require extensive ground testing before they are certified to fly. In the hypersonic regime, ground testing will be critical because of the complexity of the flow interactions and the inability of the modeling to capture transition to turbulence, nonequilibrium molecular states, and unsteady shock and combustion phenomena. The testing requirement cannot currently be satisfied at high Mach numbers because there are no facilities that can run higher than Mach 7 or so with true flight conditions for longer than ten milliseconds. That limit occurs because the plenum temperatures must exceed 3000K. Now a new approach with a lower temperature plenum and electron beam heating downstream of the throat appears to be possible and is being explored by a team under Air Force (Arnold Engineering Development Center) support including Princeton University, Lawrence Livermore Laboratory, Sandia National Laboratories and MSE Technology Applications, Inc. Testing at the 1 MW level is under way and plans are being formulated to build a Mach 12 facility with 200 MW of electron beam energy addition. Electron beams are also the most efficient way of establishing conductivity in cold air, and with their use, MHD power extraction, flow control and inlet optimization may now be possible. This talk will present the current state of these technologies and discuss their future impact.

November 12, 2002
3:30 pm (Tuesday)

Note unusual date and time

Dr. Isao Shimamura
Institute of Physical and Chemical Research (RIKEN), Japan

Dynamics of Antiprotonic Atoms

Antiprotonic atoms, a kind of exotic atoms, are the atoms in which an electron is replaced by an antiproton, or the antiparticle of the proton. The antiprotonic atoms may be
regarded as peculiar diatomic molecules with a pair of positive-charge and negative-charge "nuclei," and have extraordinary properties. They are in resonance states, rather than in stable bound states. Just after an antiprotonic atom is formed in a collision of an antiproton with an ordinary atom, the antiproton is in an orbital with a large principal quantum number (around ~40), and then cascades down to lower and lower orbitals via various atomic processes, such as radiative transitions, Auger-electron emission, and collisions with ambient species. The antiproton decays when it encounters the nucleus in the antiprotonic atom, the lifetime against the decay being usually of the order of picoseconds. For a few percent of antiprotonic helium only, and not for any other kind of antiprotonic atoms, the lifetime is six orders of magnitude longer. Recent experimental findings about and theoretical understanding of these strange exotic atoms, their formation process, and the atomic processes they experience before their decay will be discussed in comparison with the much-better-known dynamics of ordinary atoms.

November 21, 2002
4:30 pm (Thursday)

Prof. Rocco Schiavilla
Old Dominion University

Parity-Violating Effects in Few-Nucleon Systems

December 5, 2002
4:30 pm (Thursday)

Dr. Alan Garscadden
Wright Patterson Air Force Laboratory

Air Force Propulsion Research Overview, and in particular, Cross Sections for Collisions by Electrons and by Ions on Hydrocarbons

The AF research and development programs on propulsion are centered around two large development programs called IHPTET and IHPRPT for turbines and rockets respectively. However there are many allied efforts such as ignition, thermal management and electrical propulsion that relate to fuels and often involve plasma interactions. This research and its imperatives will be outlined. Studies providing a reliable data base for plasma effects on fuels will be presented in more detail. This research uses a versatile high resolution Fourier Transform Spectrometer system. Results will be presented for octane and for decane.