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Department of Physics and Astronomy
Seminars/Colloquia, Fall 2004

Unless noted otherwise, Tuesday Colloquia are at 4:00 pm
with refreshments served 15 minutes before each colloquium.

Scheduling for additional seminars will vary.

Abstracts of Talks

Robert Kroeger Department of Physics and Astronomy University of Mississippi Study of B → D20(2460) π- and B → D10(2420) π- We report on our study of B mesons decaying into one of the narrow p-wave charm resonances, D20(2460) π- and D10(2420) π-. These events were collected by the BABAR detector at the PEP-II asymmetric B Factory. Our study will be useful in the investigation of the properties of the Heavy Quark Effective Theory (HQET).

Wing Lau Department of Physics University of Oxford Application of Finite Element Design in Physics

Chris Mullen Department of Civil Engineering, University of Mississippi Director, Center for Community Earthquake Preparedness Seismic Vulnerability of Essential Facilities in North Mississippi An overview of earthquake vulnerability issues affecting Mississippi is given in the context of the built environment. Work at the Center for Community Earthquake Preparedness (CCEP) is addressing these issues at a variety of levels. A number of site specific studies will be highlighted as well as a state-wide hazard mitigation project in progress sponsored by the Mississippi Emergency Management Agency. A sense of what a large magnitude event site will do to this region will be provided through presentation of artificially generated site-specific ground motions, 3D nonlinear FE simulation of building and bridge damage subject to these motions, and vibration testing of an operating interstate highway bridge.

Jerry Blazey Department of Physics, Northern Illinois University Director, Northern Illinois Center for Accelerator and Detector Development News on the Microscopic Universe from the Energy Frontier The DZero particle physics experiment at Fermi National Accelerator Laboratory offers an unprecedented look at the microscopic universe. A basic introduction to the Fermilab accelerator complex and DZero detector provides the context for current, intriguing studies of the submicroscopic world. These studies include searches for new particles and forces, the origins of mass, and possible extra spatial dimensions.

Orest Symko Department of Physics University of Utah Quasicrystals and Their Unusual Properties The discovery of the quasicrystal phase in certain solids opened the field to a new class of materials. Because of their unusual symmetry, such as 5-fold, 7-fold, 10-fold, etc... their structure and properties are of great interest. Diffraction patterns show a highly ordered solid even though the system is not periodic. In fact ordering occurs in a higher dimensional space, one being a 6-dimensional space. Their properties are also unusual: they are very strong, they have a very low coefficient of friction, and they have a non-wet surface. This can be attributed to a large extent to their atomic structure.

Roger Waxler Department of Physics and Astronomy University of Mississippi Structure in Narrow Band Near Ground Nocturnal Sound Fields: A Quiet Height at Night As the ground cools off after sundown an acoustic duct forms in the lower atmosphere. A monotone sound field propagating in this duct can be represented as a superposition of independently propagating modes, much as acoustic or electromagnetic waves in waveguides are represented. The atmosphere is, however, not stationary. In practice the modes, and the way in which they propagate, fluctuate both spatially and temporally. Nonetheless, it has been predicted theoretically, and validated experimentally, that in the first few meters of the atmosphere the mode shapes are stable. Further, a few hundred meters or more from a monotone sound source the propagating field has a generic and stable vertical structure near the ground: there is a robust minimum in sound level at a fixed height, typically a few meters from the ground. This height decreases with increasing frequency more rapidly than 1/f.

John Foley Department of Physics and Astronomy Mississippi State University The Transmission of Dipole Radiation Through Interfaces and the Anti-Critical Angle Radiation emitted by an electric dipole consists of traveling and evanescent plane waves. Usually, only the traveling waves are observable by a measurement in the far field, since the evanescent waves die out over a length of about a wavelength from the source. We show that when the radiation is passed through an interface with a medium with an index of refraction larger than the index of refraction of the embedding medium of the dipole, a portion of the evanescent waves are converted into traveling waves, and they become observable i n the far field. The same conclusion holds when the waves pass through a layer of finite thickness. Waves that are transmitted under an angle larger than the so-called anti-critical angle are shown to originate in evanescent dipole waves. In this fashion, part of the evanescent spectrum of the radiation becomes amenable to observation in the far field. We also show that in some situations the power in the far field coming from evanescent waves greatly exceeds the power originating in traveling waves.

Sabine Hossenfelder Department of Physics University of Arizona Planck Scale Physics Planck scale physics represents a future challenge, located between particle physics and general relativity. The Planck scale marks a threshold beyond which the old description of spacetime breaks down and conceptually new phenomena must appear. Little is known about the fundamental theory valid at Planckian energies, except that it necessarily seems to imply the occurrence of a minimal length scale, providing a natural ultraviolet cutoff and a limit to the possible resolution of spacetime. Motivated by String Theory, the models of large extra dimensions lower the Planck scale to values soon accessible. These models predict a vast number of quantum gravity effects at the lowered Planck scale, among them the production of TeV-mass black holes and gravitons. Within the extra dimensional scenario, also the minimal length comes into the reach of experiment and sets a fundamental limit to short distance physics. My talk will focus on the effects at energies close to the lowered Planck scale within the effective models of Large Extra Dimensions.

Thomas Marshall Department of Physics and Astronomy University of Mississippi Do Cosmic Rays Initiate Lightning Flashes? In 1925 C. T. R. Wilson (Nobel Laureate in Physics for developing the cloud chamber) first suggested that an energetic electron in a strong thunderstorm electric field would gain more energy from the field than it loses in collisions; such electrons are now called "runaway" electrons. Gurevich et al. [1992] suggested that an avalanche of runaway electrons, called runaway breakdown, might initiate a lightning flash. They suggested that runaway electrons have energies on the order of 1 MeV. The 'seed' electron for such an avalanche is assumed to be a cosmic ray secondary. In this colloquium I first review the way in which runaway breakdown is hypothesized to occur. Then I present recent in-cloud electric field (E) measurements and inferred lightning initiation locations of three cloud-to-ground lightning flashes. These data are among the first to identify a thunderstorm region in which the preflash E exceeded various theoretical runaway electron threshold values. The maximum measured E in the region was 186 kV m-1 at 5.77 km altitude, which for runaway electrons is equivalent to 370 kV m-1 at sea level; this E value is 130-183% of various estimations of the runaway breakdown threshold. In addition, the volume where E exceeded the runaway thresholds was estimated to be 1-4 km3, with a vertical depth of 1000 - 1200 m. At least within part of this volume (and perhaps in most of it) the characteristic scale height for exponential growth of runaway electrons was 100 m or less. Thus, the main result of this study is that for these three flashes the conditions necessary for runaway breakdown existed, so cosmic rays could have initiated the flashes. I will also show a few examples of unusual electric discharges inside clouds that may also have been initiated by cosmic rays.

Tom Weiler Department of Physics and Astronomy Vanderbilt University Far-Out Neutrinos: a New Kind of Astronomy Neutrino telescopes, proposed and under construction, should map out the neutrino sky, analogous to the way the electromagnetic sky has been mapped for centuries. Like light and unlike cosmic-rays, the neutrinos will point back to their sources. But unlike light, the neutrinos are not attenuated at high energies and so will allow us to see farther into space and time, and deeper into sources. In this colloquium we illustrate with specific examples the promise which neutrino astronomy at energies at and above 100 TeV holds to study astrophysics, particle physics, and maybe even cosmology.