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Time: |
Fridays, noon-1:00pm |
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Place: |
Room 206 (unless otherwise noted), Science and Tech I |
Hydrodynamic
experiments on the Nike Laser
Abstract:
Inertial confinement fusion with lasers
is a promising path to fusion energy.
Hydrodynamic instabilities arise during compression of fuel pellets
needed to achieve fusion. The Nike laser
is well suited for studying such instabilities and ways of mitigating
them. Using laser ablation on Nike,
targets can be shocked to ~10 Mbar pressures and accelerated to ~100 km/s in
the course of 4 ns. This talk will give
an overview of the laser and focus on some recent hydrodynamic experiments and
associated diagnostics.
October 7: Jeffrey Urbach – Chair
& Associate Professor of Physics,
Shaking and shearing in a vibrated granular layer
Abstract:
I will discuss experiments and computer simulations of thin layers of uniform
spheres on a smooth horizontal plate that is oscillating vertically. This
system provides a simple but striking demonstration of some of the unusual
phenomena associated with excited granular media (e.g. shaken sand). The
energy input from the vibrating plate causes the spheres to collide
chaotically, much like the molecules in a gas. Several phase transitions are
observed, some closely analogous to transitions seen in equilibrium
thermodynamics. In particular, a single layer of spheres ‘melts’ in a
transition that displays the characteristics of a Kosterlitz-Thouless
transition, and geometric confinement produces a surprising phase diagram very
similar to that observed in colloidal suspensions. However the energy
flow required to keep the granular particles in motion
process leads to some remarkable non-equilibrium effects, including spontaneous
segregation into phases with dramatically different ‘temperatures’. I
will also describe recent measurements of the role of the depletion force in
granular mixtures and of the effects of an imposed shear on the granular layer.
October 14 (in Room 310, ST 1): Elizabeth J. Beise – Professor of Physics,
Strange
and Not so Strange things about the Proton
Abstract:
It has been over 60 years since the Nobel Prize was awarded to Otto Stern for the discovery that the proton has an anomalously large magnetic moment, nearly three times what one expects from a spin-1/2 point particle. This was one of the first hints of the underlying quark-gluon structure of the protons and neutrons that make up the bulk of the visible mass of our universe. The now well-established theory of Quantum Chromodynamics describes the strong interaction between quarks and the gluons that bind them, and accounts for many of the observed bound states that are seen in nature. But there are still many unanswered questions, such as how the electromagnetic properties arise in these bound states. In this talk I'll present an overview of where we stand today in our understanding of nucleon electromagnetic properties, as well as a more detailed look at the use of parity violation in electron scattering to specifically pin down the contribution of strange quarks to the proton's charge and magnetism.
October 21: Weihsueh Chiu
– Environmental Scientist, U.S. Environmental Protection Agency, Washington, DC
More info
Application of
Mathematical Methods from Physics to Pharmacokinetics (Reflections of an Errant
Physicist in the Biological Sciences)
Abstract:
Pharmacokinetics is the study of
the absorption, distribution, metabolism, and excretion of chemicals in the
body. By enabling one to relate (more
easily measured) external chemical exposures to (more difficult to measure)
internal chemical concentrations at the site(s) of toxicity, the understanding
of the pharmacokinetics of environmental chemicals is a key element of
assessing their potential human health risks.
There are a variety of mathematical modeling methods for analyzing
pharmacokinetic data – many of which have analogous applications in other
fields including physics and cosmology. The
continuum of such methods ranges from simple analytic models requiring no more
than the “back-of-the-envelope” to numerical models requiring weeks or more of
computer simulation time, with a tradeoff between the ability to intuitively
understand a model and its fidelity to the system under investigation. Examples of current research at U.S. EPA in
pharmacokinetics utilizing such models are presented, and demonstrate a role
for modeling approaches across this continuum.
An examination of the steady-state limit for pharmacokinetic models for
use in extrapolating between routes of exposure (i.e., oral to/from inhalation)
exemplifies the sometimes surprisingly broad utility of simple analytic
solutions. At the other end of the
continuum, an ongoing analysis of human pharmacokinetic data on
trichloroethylene, an organic solvent that is a common environmental
contaminant, requires use of a numerical simulation model along with a Bayesian
statistical model implemented with Markov chain
Disclaimer: The views expressed in this presentation are those of the author and do not necessarily reflect the views or policies of the U.S. EPA.
Nov. 4: Tom Gentile – Research
Scientist at the National
Polarized 3He: A Gas for All Seasons, but Still Mysterious
Abstract:
In the four decades since its first observation, applications of nuclear
spin-polarized 3He gas have taught us about interplanetary magnetic
fields, quantum statistics, and the structure of nucleons, and more recently is
being applied to magnetic resonance imaging and neutron physics. After surveying these topics and introducing
the two optical pumping methods for orienting the nuclei in 3He gas,
emerging applications in neutron spin filters will be presented. These include the study of magnetic materials
by neutron scattering, studies of nucleon-nucleon interactions, and precision
low energy tests of the standard model.
Turning to the spin-exchange optical pumping method for polarizing the
gas, we find that recent work has substantially changed our understanding of
the polarization limits and relaxation sources, and yielded new unanswered
questions. Although advances in
spectrally narrowed lasers and storage of the polarized gas have allowed us to
obtain 75% 3He polarization in large volume neutron spin filter
cells, the basic rate balance model predicts that we should be observing nearly
100%. The culprit appears to be an unexpected and currently unexplained form of
relaxation that limits the polarization. In addition, studies of the glass
storage vessels have revealed unanticipated, complex magnetic behavior.
Nov. 18 (in Room 310, ST 1): Vincent
Urick – Research
Scientist at the Naval Research Laboratory,
Optoelectronic Oscillators for Microwave
Photonic Applications
Abstract:
An optoelectronic oscillator is a ring oscillator comprising a fiber-optic link closed upon itself. Optoelectronic oscillators provide a novel solution for many microwave photonic applications, including tunable, spectrally-pure microwave and millimeter-wave generation, mode-locked optical oscillation, and carrier recovery for signal processing techniques. Present state of the art optoelectronic oscillation performance is outlined and significant improvements are suggested, concentrating on long-haul analog link research. Novel techniques for mitigation of round-trip loss, chromatic dispersion, and stimulated Brillouin scattering are demonstrated, the results of which have strong bearing on future optoelectronic oscillator performance capability.
December 2: Allen Garroway – Research Scientist
at the Naval Research Laboratory,
Origins
of MRI- A Personal View
Abstract:
Magnetic
Resonance Imaging (MRI) is now a well-accepted medical procedure. The
superbly engineered modern MRI systems and the massive medical community that
interprets MRI scans tend to obscure the history of the beginnings of MRI, in
rather modest research facilities in the early 1970s. That seminal work
at SUNY Stony Brook and the
As a participant
in the earliest work on MRI at the
December 9: Eddie Guerra – Associate Professor of Physics,
TBA
Questions about the physics seminar? Contact Karen Sauer at ksauer@physics.gmu.edu
Other interesting seminar series at GMU:
Computer Science Department
Seminars
Research Colloquium: Computer Design of Materials
School
of Computational Science Colloquia
Quantum Information Science (QIS) Seminar
Physics Seminar Schedule for previous years: Fall01 schedule, Spring02 schedule, Fall03 schedule, Spring04 schedule, Fall04 schedule, Spring05 shedule