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University of Wyoming

University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Cinnamon Room, PS 237

Fall 2006 Schedule

Oct 6 John Bally (U. Colorado)
Star Formation in Clusters: The Birth Environment of Planetary Systems?

Observations demonstrate that most stars are born in short-lived clusters or multiple star systems. Many form within a few parsecs of massive stars which produce intense UV radiation and die in supernova explosions. Thus, during their first few million years, forming planetary systems are likely to experience dynamical perturbations from passing sibling stars, become exposed to intense UV radiation fields, and be peppered by supernova ejecta containing short-lived radioactive species. I will discuss some recent results including: - New constraints on massive star formation in Orion. - The impact of Orion-like environments on planet formation. - The importance of star-formation feedback.

Oct 20 Jeremy Darling (U. Colorado)
Tunneling, Masing, and Dasing Insights into Galaxy and Black Hole Evolution, Cosmology, and Fundamental Physics

The quantum structure of simple molecules can produce pathological behavior in common natural settings, providing astronomers with useful astrophysical probes.

The most striking pathology is molecular maser emission, which can exhibit brightness temperatures in excess of 10^15 K. The extreme brightness temperatures and small scales of molecular masers make them excellent probes of distance scales, the ionized interstellar medium, and gas kinematics in starbursts and around massive black holes. "Umbrella" inversion tunneling in ammonia can also mase, and in absorption provides a natural molecular gas thermometer.

Molecules can conversely be coaxed into stimulated absorption. For example, OH produces "conjugate" lines: one line is a maser and the conjugate line forms an anti-maser; the net energy budget is null. These lines indicate the molecular gas density and provide precise determinations of the value of physical constants at arbitrary redshift. Formaldehyde (H2CO) can produce the ultimate "anti-maser" in which line excitation temperatures are cooled below the local cosmic microwave background (CMB) temperature. Because the CMB (by definition) covers the sky and lies behind every galaxy, H2CO absorption can be detected at arbitrary redshift and does not rely on the fortuitous alignment of foreground molecular clouds with background flat- or inverted-spectrum radio sources. Moreover, H2CO is a "Swiss Army Knife" molecule for gastrophysics, providing measurements of molecular gas density, total molecular gas mass, astrochemistry pathways, and line excitation, rotation, and kinetic temperatures. Formaldehyde will be a molecule of choice for ALMA and EVLA observations of dense molecular gas from present day to the early universe.

Oct 27 Dennis Ebbets (Ball Aerospace)
The Deep Impact Mission and Careers in Aerospace

The American aerospace industry is a major employer of scientists and engineers, and should be considered as an attractive career opportunity for students of physics, astronomy, mathematics, computer science, chemistry, and virtually all engineering disciplines. It offers opportunities to work on space hardware for leading edge scientific investigations, assets crucial to our nation's defense, and a growing number of commercial enterprises. This discussion will describe what scientists actually do for such companies, offer perspectives on the nature of the industry and the work environment, and some suggestions for finding and applying for a position. The speaker has an academic background in physics and astronomy, and has spent nearly 22 years at Ball Aerospace & Technologies Corp. in Boulder, Colorado. On July 4, 2005 one of NASA's most dramatic space missions reached its climax when the Deep Impact spacecraft collided with comet Tempel 1 at about 10 km/sec (nearly 24000 miles per hour). The impact excavated a fresh crater and launched a plume of debris that was studied intensively by the companion flyby spacecraft, and by an armada of telescopes in space and on the earth. For the scientists who proposed the mission it is an opportunity to study pristine material left from the earliest days of the formation of our solar system. This talk will describe the scientific objectives, the mission design and the early results of the successful impact.

Nov 3 Geoff McHarg (Air Force Academy)
A Brief History of Sprites---Lightning in the Mesophere

Sprites are very brief (~ms) luminous events which take place in the mesosphere. Sprites have sometimes been referred to as lightning in the mesosphere, but while linked to traditional tropospheric lightning, sprites are a separate phenomena. This talk will give a brief history and tutorial of sprite physics, including measurements made of sprites at the Wyoming Infrared Observatory in 1998 and 2006.

Nov 16 Mikhail Zamkov (U. Illinois)
Ultrafast spectroscopy of carrier dynamics in carbon nanotubes

I will touch two topics in my talk: (i) Formation of long-lived image states around carbon nanotubes and (i) electronic excitations lifetime in multiwall carbon nanotubes. The first topic is related to the formation of long-lived electronic states with wave functions enclosing a carbon nanotube. We observe these states, for the first time, in our two-color time-resolved photoemission experiments. These cylindrical electronic rings constitute a new class of surface image states due to their quantized angular motion. The electron rotation about the axis of the nanotube gives rise to a centrifugal force that virtually detaches the electron charge-cloud from the tube's surface. This isolation results in enhanced lifetimes that were measured to be one order of magnitude longer than those of image states forming above metal surfaces. The second part of my talk is related to the question of whether electrons form a Fermi liquid or a Tomanaga-Luttinger liquid in multiwall nanotubes. Despite the structural similarity between the single and multi walled nanotubes (SWNTs and MWNTs), the nature of electron transport in these systems was found to be fundamentally different. In contrast to a SWNT, where conduction electrons are constrained to interact in a strictly one-dimensional manner (Tomonaga-Luttinger-liquid system), electron excitations in a MWNT exhibit a distinct multi-dimensional Fermi-liquid behavior.

Nov 17 Margaret Hanson (U. Cincinati)
Revealing our Galaxy's Massive Star Clusters

Ironically, it is far more difficult to map out the massive star content of our own Milky Way Galaxy than in other galaxies. Consequently, little is known about massive stars and massive star clusters presently lurking in the Milky Way's inner disk. I will begin by presenting recent results which show we are missing far more than we ever realized. I will discuss infrared-based observational methods I am developing to search our Galaxy for massive star clusters. If such examples can be found, they provide realistic, resolvable analogues to super star clusters found in distant galaxies and which can only be studied by their integrated light. Massive young clusters can also serve as bright beacons within our Galaxy's disk, allowing us to trace our Galaxy's spiral arms and possibly measure the Galaxy's rotational dynamics

Nov 20 Jinke Tang (U. New Orleans)
Is magnetite a half-metal?

Half-metal families such as CrO2, Fe3O4 and La2/3Sr1/3MnO3 attract attention owing to their speculated 100% spin polarization P according to electronic structure calculations. They are conductors for one spin channel and insulators/semiconductors for the other spin channel and have potential applications in spin electronic devices. On the experimental side, these materials fail to show high value of P for a variety of reasons including oxidation, disorders and defects, particularly on the surfaces. We show that polystyrene coated Fe3O4 nanoparticles exhibit intergranular tunneling magnetoresistance of 22.8% at room temperature and a maximum MR of 40.9% at 110 K. The spin polarization P is about 54% and 83%, respectively. High spin polarization is retained at the surface by the polystyrene coating, which prevents the oxidation of Fe3O4.

Dec 4 C.V. Ramana (U. Michigan)
Designing New Materials for the Future: Challenges in the Energy Technology

The recent interest in the energy technology has generated a strong interest in rechargeable lithium-ion batteries and fuel cells, which are being considered as the most advanced energy-storage and conversion devices. However, the grand challenges facing the scientific community in this field are the discovery, design, and development of new materials to meet the requirements of enhanced performance, stability, long-shelf life, and environmental safety. Much new science awaits its discovery, particularly at the reduced dimensions, and novel fabrication strategies remain to be explored in order to address these challenges. The present talk will focus on the critical issues in developing novel intercalation materials for application in energy storage and conversion applications. The key idea developed to fabricate thin films of LiNi_[1-y] Co_y O_2 (y<1) system, which is not at all possible otherwise, along with the results on their structure and properties will be presented. New electrode materials, which are relatively unknown, based on Fe oxides will also be discussed in relevance to their application in lithium-ion batteries. The emphasis is to show that there are extensive opportunities for utilization of these materials in extremely diverse fields of technology, including medicine, where high ratings, enhanced performance, and long-shelf lives are required.

Dec 8 Karen Leighly (U. Oklahoma)
Low-ionization Line Emission in Quasars

Quasars can be recognized by the strong, broad emission lines in their rest-frame optical and UV spectra. These emission lines are used to estimate black hole masses and gas metallicities, and these estimates are propagated broadly throughout astrophysics and cosmology. In this talk I will describe recent research on understanding low-ionization emission lines. I will first describe a study of the distribution of FeII/MgII in narrow-line Seyfert 1 galaxies from the Sloan Digital Sky Survey. This work leads us to conclude that there is a real dispersion in the FeII emission that is probably a consequence of a range of excitation of this set of lines. I will also describe resesarch on the unusual intrinsically X-ray weak quasar PHL 1811, and the consequences of illuminating gas with a very soft spectral energy distribution. I will conclude with a brief description of future directions.

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006
Contact for program information: Daniel Dale (ddale @