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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

Spring 2005 Schedule

Jan 21 Kelly Page
Application of Linear Predictors in Adaptive Optics

The goal of adaptive optics (AO) systems for astronomical telescopes is to remove the distortions caused in optical images by the turbulent atmosphere above the telescope. This technology has blossomed in the 1990\x{2019}s and has ushered in an era of giant telescopes that are expected to exceed 50 m in diameter. This technology has proven to be enormously valuable in astronomy, which drives scientists for even better AO systems. In this work, we will demonstrate how an AO system can be improved by employing a turbulence prediction algorithm based on the frozen flow model of atmospheric turbulence. In the frozen flow model turbulence is treated as a collection of discrete static layers, each being translated by a different layer velocity.

Feb 4 Eric Hallman (U. Colorado)
Clusters of Galaxies as Probes for Precision Cosmology

I critically assess the role of clusters of galaxies as probes for precision cosmology. Using synthetic observations of simulated clusters viewed through their X-ray emission and thermal Sunyaev-Zeldovich effect (SZE), we have reduced the observations to attain measurements of the cluster gas mass. We utilize both parametric models such as the isothermal cluster model and non-parametric models that involve the geometric deprojection of the cluster emission assuming spherical symmetry. We are thus able to quantify the possible sources of uncertainty and systematic bias associated with the common simplifying assumptions used in reducing real cluster observations including isothermality and hydrostatic equilibrium. I address the key question: What is the best way to measure cluster masses with precision in order to do cosmology?

Feb 24 Saiful I. Khondaker (U. Texas)
Fabrication and electron transport properties of nanodevices containing individual chemical nano-structures

Nanostructures made by chemical synthesis such as nanocrystals and molecules have attracted tremendous attention as they constitute promising building blocks for future generation of electronic devices and model systems to investigate novel quantum transport phenomena in confined geometries. Probing the electronic properties of individual nanostructures is challenging as it requires (i) nanometer spaced electrodes, and (ii) placement of the nanostructures between the electrodes. We pioneered a remarkably simple and highly reproducible method for the fabrication of metallic electrodes with sub-5 nm separation in ambient environment on Si/SiO2 substrate. Commercially available bare gold colloidal nanoparticles are first trapped between prefabricated large-separation electrodes to form a low-resistance bridge (or "nanoscale fuse") by an AC electric field. A DC bias voltage is then applied to break the bridge via current induced electromigration to produce nanometer spaced electrodes. In this talk, I will present the fabrication technique of the nanospaced electrodes and present electrical transport measurements of two sets of devices made with individual nanoparticles and individual molecular wires.

In the first experiment individual thiol coated gold nanoparticles were electrostatically trapped in the nanogap to form a single electron transistor. Current - voltage (I-V) characteristic measured at 4.2 K show clear Coulomb blockade and Coulomb staircase phenomenon that can be modulated by tuning the number of electrons in the nanoparticle by applying a gate voltage. In the second experiment, individual phenylene-ethynylene molecular wires with or without NO2 side group were self assembled onto the nanospaced electrodes. The low- bias I-V characteristics measured at 4.2 K could be switched between different stable configurations, some of which show negative differential resistance, and has been observed in molecules irrespective of their NO2 functionalization. We explain this as a possible demonstration of either conformational changes in the molecules or a change in coupling of the molecular junction.

Feb 28 P. K. Babu (University of Illinois at Urbana-Champaign)
Electronic Properties of Metal Nanoparticles and Carbon Nanohorns - Revealed by Solid State NMR

Nanoscale systems are now attracting worldwide attention and fundamental research in this field is required not only to enhance our understanding but also to tailor their properties for future technological applications. Traditionally, nuclear magnetic resonance (NMR) experiments have played a crucial role in elucidating the electronic properties of a variety of bulk materials. Application of NMR to nanoscale systems is also proving to be extremely rewarding. In this talk, I will describe how solid state NMR experiments help us to understand the electronic properties of nanoparticle catalysts and carbon nanohorns. I will also discuss about quantum size effects on the distribution of local density of states in Pt nanoparticles, probed by low temperature NMR experiments.

Mar 4 Martin Gaskell (U. Nebraska)
Reddening of Active Galactic Nuclei

The ultra-violet spectra of quasars have been widely assumed to be unreddened, yet in the optical and IR active galactic nuclei show signs of reddening. I show that the solution to this paradox is that the dust in active galactic nuclei is unlike any hitherto known. This dust has been substantially modified by the harsh environment of the AGNs. Reddening of AGNs has wide-ranging implications both for understanding how black hole accretion works and the role of AGNs in galaxy formation. The continuum spectral energy distributions of different types of AGNs are not radically different. This supports unified pictures of accretion power from scales of stellar mass objects up to supermassive black holes. The presence of dust means that AGNs are more plentiful and more luminous than has hitherto been thought. This has implications for the formation of supermassive black holes in the nuclei of galaxies in the early universe.

Mar 11 Mike Brotherton, Danny Dale, Chip Kobulnicky and Mike Pierce (U. Wyoming)
Overview of Current UW Astronomy Research

This week features UW Professors Mike Brotherton, Danny Dale, Chip Kobulnicky, and Mike Pierce who will give overviews of their research activities. Areas as diverse as cosmology, quasars, galaxy clusters, star formation, planet formation, and astronomical instrumentation will be discussed. UW undergraduates are especially invited to attend to learn about astronomy research possibilities at Wyoming.

Apr 8 Neil Cornish (Montana St.)
Gravitational Wave Astronomy and the LISA Observatory

The Laser Interferometer Space Antenna (LISA) will be the first in a new line of Great Observatories, following in the footsteps of the Hubble, Compton, Chandra and Spitzer space telescopes. Unlike her predecessors, LISA will not produce any images nor record any spectra, but like a giant spider on a vast web, LISA will detect the faint vibrations caused by massive bodies colliding throughout the Universe. As the first space observatory to study the Universe using gravitational waves, LISA has tremendous science potential, ranging from the study of galaxy evolution using supermassive black hole mergers, through tests of general relativity, to the placing of constraints on stellar population synthesis models by providing a census of several thousand compact galactic binaries. The presentation will describe the LISA mission and some of the science goals, and explain what it means to be a gravitational wave astronomer.

Apr 22 Karen Kinemuchi (Wyoming)
AB-Type RR Lyraes in the Northern Sky Variability Survey

RR Lyrae variable stars are important astronomical objects for the investigation of the structure and the evolution of the Milky Way Galaxy. These pulsating stars are known to be found in old stellar populations in our Galaxy and have the useful feature that we can readily derive distances from them. The Northern Sky Variability Survey (NSVS), whose data was obtained through the Robotic Optical Transient Search Experiment (ROTSE-I) telescope, provides an opportunity to study RR Lyraes found in the Solar neighborhood. These stars can probe the inner halo and thick disk component of the Galaxy. We have found 1203 ab-type RR Lyraes (RRab) stars in the NSVS database and have determined the periods, amplitudes, mean magnitudes, and photometric metallicities. Furthermore, we have assigned the RRab stars into Oosterhoff I and II groups, as well as identify a metal-rich group, which is our thick disk sample. Analysis of the RRab stars in these groups will be discussed.

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