Department of Physics and Astronomy


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 2004 Schedule

Sep 17 Michael Hauck (Western Research Institute)
Remote Sensing Applications in Transportation: Applying Physical Principals to Improve the Nation's Infrastructure Efficiency and Performance

The application of remote sensing technologies to America's transportation infrastructure management holds immense promise to improve the safety, efficiency, flexibility, and cost-effectiveness of the transportation system - a 1.3 trillion dollar asset on which taxpayers spend over 117 billion dollars per year. Remote sensing technologies use acoustic and electromagnetic waves from various parts of the energy spectrum that can accentuate physical and chemical properties of materials (and therefore engineering performance), especially when used in combination. Remote sensors can be deployed on platforms ranging from satellites to construction equipment. Specific applications include the surveying of construction obstacles to avoid damaging buried infrastructure, the non-destructive testing of new pavements for quality control during construction, and the detection of precursors to infrastructure failure that could be used to schedule preventive maintenance. In this talk I will describe a research program jointly sponsored by NASA and the US Department of Transportation intended to kick-start an industry that will commercialize remote sensing products and technologies to address the Nation's critical transportation issues.

Sep 24 Jerry Tastad (Wyoming)
Adventures of Amateur Radio

Jerry is the Lab Coordinator for the University of Wyoming Department of Physics & Astronomy. He has been an amateur radio operator for over forty years and currently holds an amateur extra-class license. Jerry will talk about the physics of amateur radio and his experiences in the field.

Oct 1 Nathan Smith (U. Colorado)
Eta Carinae and its Massive Circumstellar Nebula

Eta Carinae is the most massive star that is close enough to be studied in detail, and it is surrounded by CNO-processed material ejected by the star in the last 160 years. The star teeters near the Eddington luminosity limit, causing erratic variability and extreme mass loss. The nebula has a huge amount of mass -- more than about 10 Msun -- which has important implications for post-MS evolution atop the HR Diagram. Additionally, the nebula around Eta Carinae provides our nearest example of the circumstellar environment of a potential hypernova progenitor, and may even raise questions about the first stars that formed in the early Universe.

Oct 29 Jordanka Zlatanova (U. Wyoming)
Chromatin fibers: one-at-a time

DNA in the nucleus of eukaryotic organisms is organized as chromatin, a DNA-protein complex that packages the huge amount of DNA into a small volume and allows for regulation of biochemical processes that need access to the information stored in the double-helical structure of DNA. The study of chromatin structure and dynamics has entered a new phase, as a result of the advent of single-molecule techniques. I will present some of our results obtained with the Atomic Force Microscope (AFM), optical tweezers (OT) magnetic tweezers (MT), and more recently with single-pair Fluorescence Resonance Energy Transfer (spFRET). AFM imaging and quantitations have led us to question the accepted solenoid model for the higher-order organization of the chromatin fiber and to suggest that the fibers possess rather irregular three-dimensional structures that can be modeled using the known dimensions of the core particle and straight DNA linkers. Optical tweezers were used to mechanically stretch individual chromatin fibers directly assembled in the flow cell of the apparatus. The force-extensions curves recorded during stretching had numerous discontinuities interpreted as individual nucleosome unraveling events. The forces needed to unwrap the DNA from around the histone octamers were in the range of 20-40 pN, the same range of forces developed by RNA polymerases threading the DNA double helix during transcription. This fact is interpreted to mean that polymerases themselves may be in the position to clear nucleosomes out of the way for transcription to occur. I will briefly mention our data on using magnetic tweezers to follow assembly of individual chromatin fibers as a function of the force applied to the DNA template. The process of nucleosome assembly is highly force-dependent and can only proceed to forces of up to 10 pN. The physiologically-relevant interpretation of the data addresses the issue of whether and under what conditions nucleosomes can reform in the wake of the passing polymerase complex. Finally, I will illustrate the use of spFRET to study fast, long-range, reversible conformational transition in the nucleosome particle.

Nov 5 Michael Meyer (U. Arizona)
Formation and Evolution of Planetary Systems: Placing Our Solar System in Context

Over the past 15 years abundant evidence has emerged that many (if not all) stars are born with circumstellar disks. While concensus is emerging concerning the the early evolution of accretion disks (tau < 10 Myr) and the characterization of older debris disks (tau > 1 Gyr) continues at a rapid pace, little is known about the transition between these two extremes thought to occur during the epoch of planet formation. The goals of our Spitzer Legacy Science Program are to trace the evolution of planetary systems from: (1) 3-10 Myr when stellar accretion from the disk terminates; through (2) 10-100 Myr when planets achieve their final masses via coalescence of solids and accretion of remnant molecular gas; to (3) 100-3000 Myr when the final architecture of solar systems takes form and collisions between remnant planetesimals produce observable quantities of dust. Our strategy is to use carefully calibrated spectral energy distributions and high-resolution spectra to infer the radial distribution of dust and gas surrounding a sample of 330 solar-like stars distributed uniformly in log- age over 3 Myr to 3 Gyr. This approach should provide insight into the diversity of planetary system architectures, contraining the range of possible outcomes of the planet formation process - thus helping to place our own solar system in context. We will report on the latest results from our program.

Nov 12 Joe Collins (Colorado)
The Role of High-Velocity Clouds in Galactic and Local Group Evolution

Since their discovery by Muller, Oort, & Raimond (1963), the objects known as high-velocity clouds (HVCs) have been the subject of much controversy. Normally detected through their HI 21-cm emission, these objects have no stellar component, and thus their distances are highly uncertain. The favored paradigm identifies HVCs as either outflows or remnant building blocks of structure formation in the Galactic Halo. Alternate hypothesis place these objects at large distances from the Milky Way, tracing cosmological structures within the Local Group. In this talk, I will review our recent work utilizing FUSE and HST UV spectra concerning the nature of these objects.

Dec 3 Charles Danforth (Colorado)
Warm and Hot Gas in the Local Universe

Sight lines to distant quasars show absorption from intervening clouds of otherwise-invisible intergalactic gas. Until recently, this Lyman-alpha forest has been observable only at high redshifts where the Lyman alpha transition (1216 angstroms) is redshifted into the visible range. In the last ten years, HST and FUSE have allowed us to access to the Lyman alpha forest at low redshift and to finally study the local, 'mature' intergalactic medium (IGM). I will discuss our study of higher-order Lyman lines from which accurate measurements of neutral hydrogen in the IGM can be made. More interestingly, we have found many counterpart absorption systems in OVI, CIII, and other highly ionized species. These ions trace a warm-hot component (T=10^5-10^6 K) rather than the warm neutral component (T~10^4 K) traced by HI. The combination of these two IGM phases (warm and hot) tells us a great deal about the structure of the local universe and some of the processes involved.

Dec 10 Michal Banaszak (University of Poznan, Poland)
Probing Block-Copolymer System with Monte Carlo and Molecular Dynamics Simulations: Pressure Effects, Triblocks, Ionic-Nonionic Blocks, Low-Temperature Extra-Ordering Effects

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