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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 2007 Schedule

Sep 7

Sep 14

Sep 21

Sep 28 Karen Bjorkman (U. Toledo)
Circumstellar Disks - An Observer's Perspective

Everywhere we look in the Galaxy, we find stars with disks around them. These stars include young stars just forming, older stars in the middle of their lives, and evolved stars that are near the end of their stellar lifetimes. As one might suspect, the properties of disks around different types of stars can be quite different. However, many of the underlying physical mechanisms are similar. Furthermore, some disks are known to vanish and reappear, and the way that this happens is not well understood. Time variability and time scales for such changes are thus important to determine. This talk will examine the various types of circumstellar disks, and discuss the techniques of observational astrophysics that can be used to determine their physical characteristics and the time scales for variability. The implications of the presence of these disks for possible planet formation will also be considered briefly.

Oct 5

Oct 12

Oct 16 Riccardo Giovanelli (Cornell U.)
ALFALFA: HI Cosmology in the Local Universe

For the last 25 years, the 21 cm line has been used to investigate the large-scale structure of the Universe, its peculiar velocity field and the measurement of cosmic paramaters. In February 2005 a blind HI survey of 7000 square deg. of sky was started with the Arecibo radio telescope, using a 7-beam feed array (ALFA). The Arecibo Legacy Fast ALFA (ALFALFA) Survey will produce a census of HI-bearing objects over a cosmologically significant volume of the local Universe. When completed, >20,000 HI sources will be detected. ALFALFA is better than previous blind surveys by ~ one order of magnitude in both sensitivity and areal resolution. As of Fall 2007, ~ 40% of the survey observations and >15% of the source extraction are completed. Preliminary results of ALFALFA will be presented, with special emphasis on the cosmic abundance of low mass, baryon rich, optically faint halos.
Time: 4:10
Place: Classroom Bldg 141

Oct 18 John Hackwell (Aerospace Corporation)
Careers for Physicists & Engineers in Aerospace

John Hackwell is the Principal Director of the Space Sciences Applications Laboratory at the Aerospace Corporation. He will present some of the work done at The Aerospace Corporation, a non-profit company that supports the Air Force in its acquisition of spacecraft and launch vehicles. He will then talk about his experiences in the industry and answer questions about careers in arerosapce.

Time: 2:00, Thursday, October 18
Place: Engineering 3102

Oct 18 Bob Gehrz (U. Minnesota) & John Hackwell (Aerospace Corporation)
30 Years of the Wyoming Infrared Observatory

An infrared site survey conducted by the Infrared Astronomy Group at the University of Minnesota showed that the high altitude mountains to the west of Laramie, Wyoming had the potential to compete with the best infrared observatory sites in the world. This finding persuaded Derek Prowse, then Head of the University of Wyoming's Physics & Astronomy Department, to establish an infrared astronomy program at the University of Wyoming in hopes of obtaining funding for a major observatory. In 1975, the Wyoming State Legislature boldly agreed to fund pure science by appropriating $975,000 for a major infrared observatory on the condition that the National Science Foundation would provide a matching grant of $625,000. We will describe the origins of the program and its subsequent growth under the leadership of Prowse's successor, W.T. Grandy, Jr. Emphasis will be given to the activities associated with the funding, siting, construction, and operation of the Wyoming Infrared Observatory. At the time of its dedication, the 92-inch Wyoming Infrared Telescope was the largest operational infrared telescope in the world. We will present a slide show describing all aspects of the activities of the Wyoming infrared astronomy program during its early days and during construction of the observatory. Amusing video footage that originally appeared on ABC's 20/20 at the time of the dedication of the observatory will be shown. Scientific highlights of the program will be reviewed.
**Public Lecture**
Time: 7:10
Place: Classroom Bldg 302

Oct 19 Robert Gehrz (U. Minnesota)
Infrared Imaging and Spectroscopic Studies of Novae, Supernovae, and Massive Stars

The winds of novae, supernovae, and massive stars enrich the composition of the interstellar medium. Determinations of the chemical composition of nova ejecta motivated by discoveries at the Wyoming Infrared Observatory will be described. Recent observation of nova and supernova ejecta with the Spitzer Space Telescope will be presented. Massive stars are supernova progenitors and their fossil wind structures may influence the geometry of the supernova remnant that results from the collapse of the iron core of the progenitor at the end of its nuclear burning lifetime. Key information provided by panchromatic imaging and spectroscopic observations of the two most luminous and massive stellar sytems known, Eta Carina and RY Scuti, is reviewed. Contributions to our knowledge about these systems made by the Wyoming Infrared Group and the Wyoming Infrared Observatory are described. The circumstellar material is shown to contain some of the important building blocks of the solar system. Ejection events in these massive stellar systems are shown to occur at intervals of the order of a hundred years. We speculate that rotation and binarism may be involved in shaping the Post-MS winds of Eta Carina and RY Scuti.
Time: 1:00
Place: Classroom Bldg 142

Oct 26 Evan Skillman (U. Minnesota)
The Evolution of Dwarf Galaxies

I will review recent results concerning the evolution of dwarf galaxies. This will highlight how the Hubble Space Telescope has improved our view of both recent (ages less than 1 Gyr) and ancient (ages greater than 1 Gyr) star formation histories of dwarf galaxies. Recent star formation histories of nearby dwarf galaxies provide us with a tool to investigate their patterns of star formation, to measure the effects of feedback on the ISM, and to help to calibrate stellar evolution models. Ancient star formation histories of nearby galaxies allow us to test current theoretical models of the evolution of dwarf galaxies. New observations are resolving the long-standing problem of the relationship between dwarf elliptical and dwarf irregular galaxies.

Nov 2

Nov 9

Nov 16

Nov 23 Thanksgiving break

Nov 27 Fabian Heitcsh (University of Michigan)
Cooling, Gravity and Geometry: Flow-Driven Molecular Cloud Formation

The structural richness of molecular clouds and their observed linewidths indicate that they are highly dynamical. Observations suggest that in the solar neighborhood, star formation in molecular clouds is generally "rapid". This seems to be at variance with models of long-lived molecular clouds involving turbulence-controlled, "slow" star formation. A solution to this conundrum requires understanding the initial conditions of star formation in a broader frame, i.e. a closer look at the details of molecular cloud formation is necessary. A new series of numerical experiments is beginning to bridge the gap between molecular cloud and star formation. I will discuss these experiments and their observable predictions.

Dec 03 Wenyong Wang (National Institute of Standards and Technology)
Electronic Transport Characterization of Nanoscale Structures

Electrical characterization of self-assembled monolayers (SAMs) has been performed using a nanometer-scale device structure. Carrier transport through the molecular devices is investigated with the technique of inelastic electron tunneling spectroscopy (IETS). The obtained IETS spectra exhibit characteristic vibrational signatures of the alkane molecules that are incorporated into the solid-state junction, presenting direct evidence of the existence of molecular species in the device structure. Studies have also been performed on magnetic tunnel junction containing molecular components, and the observed TMR bias dependence is investigated. 1/f and RTS noise properties of semiconductor nanowire FETs will also be discussed.

Dec 06 Evgueni Nazaretski (Los Alamos National Laboratory)
Submicron Resolution Ferromagnetic Resonance Spectroscopy using Scanned Probe Magnetic Resonance Force Microscopy

Magnetic resonance force microscopy (MRFM) offers a very high sensitivity approach to detection of magnetic resonance, as well as a means of performing local resonance. Proposed by J.A. Sidles in 1991, it has been used for the detection of both electron spin resonance and nuclear magnetic resonance. Recently Rugar and co-workers reported detection of a force signal originating from a single electron spin1, emphatically demonstrating unprecedented MRFM sensitivity. Incorporating basic elements of Magnetic Resonance Imaging (MRI), MRFM can provide much higher spatial resolution than conventional MRI. Recently, ferromagnetic resonance (FMR) has been detected by MRFM in YIG bar2 and micron size permalloy dots3. Locally resolved FMR has important technological applications, and can be used for imaging of magnetic impurities and buried interfaces. In general, ferromagnetically coupled systems pose a challenge for spatially resolved FMR due to a strong interaction between the spins. The observed resonance modes typically involve precession of spins in an entire sample. In our work we focus on the regime when the effect of the MRFM tip is non-perturbative: the field inhomogeneity due to the field from the magnetic tip strongly modifies the resonance modes, and leads to the formation of local resonances under the tip. We report MRFM spectra from various ferromagnetic samples and demonstrate the capability of MRFM to perform highly localized spectroscopic studies in ferromagnets. We discuss the model which accounts for the presence of a non-uniform tip field and compare numerical simulations to experimental data

Dec 07 Hou-Tong Chen (Los Alamos National Laboratory)
Electromagnetic Metamaterials for Terahertz Applications

Development in terahertz (THz) science and technology is prevented mainly due to the deficiency of material responses at this frequency regime. The electronic and photonic responses at microwave and optical regimes, respectively, both degrade significantly at THz frequency regime. Over the last decade many efforts associated with filling this so-called \x{201C}THz gap\x{201D} have resulted in moderate progress in THz generation and detection as well as various demonstrations of promising applications. Despite these advances, functional devices to control and manipulate THz waves, which are crucial in many applications, are still largely not available. One solution to this problem is the use of a recently developed class of artificially structured composite materials termed metamaterials. The resonance responses of electromagnetic metamaterials significantly enhance their interaction with THz waves, which is a prerequisite for accomplishing necessary functional devices for THz applications, thereby providing new opportunities in advancing THz technology. We have created a series of novel planar electric metamaterials operating at THz frequencies. All of them show very strong electrically resonant response and excellent band-pass or band-stop filtering effects. Alteration of the properties of substrates upon which the metamaterials were fabricated has resulted in actively and dynamically tunable THz metamaterial devices. High efficiency all-electronic THz switching and modulation operating at room temperature have been accomplished by the use of a hybrid of metamaterial and Schottky diode structure. The THz transmission was easily and effectively switched and/or modulated by applying a relatively small voltage bias. Dynamical switching of THz radiation was also achieved by photo-doping of the semiconductor substrates, where ultrafast switching has been demonstrated by the use of ErAs/GaAs nanoisland superlattice substrates. We show that electromagnetic metamaterials are promising in building various high efficiency and frequency agile functional devices for THz applications.

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006
Spring 2007
Contact for program information: Daniel Dale (ddale @