Events at Physics |
Events During the Week of January 27th through February 3rd, 2008
Monday, January 28th, 2008
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Modern Magnetic Mirrors in Novosibirsk: New results and Their Implications for the Future
- Time: 12:05 pm
- Place: 2241 Chamberlin Hall
- Speaker: Alexander Ivanov, Budker Institute, Noisibirsk, Russia
- Medical Physics Seminar
- Evaluation of a Pressure Sensing Array for use with Ultrasound Strain Imaging
- Time: 4:00 pm
- Place: 1345 Health Science Learning Center (refreshments will be served)
- Speaker: Lee Kiessel Research Assistant, Department of Medical Physics, UW-School of Medicine and Public Health
- Abstract: Mechanical in vitro tests and in vivo elasticity imaging have shown differences between breast tissue types in their nonlinear stress/strain behavior. This information could be utilized to differentiate between benign and malignant lesions potentially reducing the benign biopsy rate. Stress and strain measurements are required for absolute measures of this non-linear behavior in vivo. A variety of tests were performed with a prototype pressure sensor array to gauge its stability, sensitivity and calibration in reference to its application in ultrasound elastography. In addition, data was collected from patients undergoing ultrasound elasticity imaging at the University of Wisconsin Breast Center. Initial tests show that the pressure sensor array is stable in an ultrasound imaging environment. A reliable calibration technique was developed, which demonstrates reproducibility to within 5% for most elements. Tests also show a wide disparity in sensitivity among elements. The most sensitive elements are capable of detecting pressure as low as about 100 Pa. Unfortunately, the average minimum detectable pressure was about 800 Pa. The most sensitive elements make the array capable of detecting initial contact and measuring the contact force during a deformation of the breast - a critical task for quantifying stress/strain nonlinearities. The preliminary clinical trial confirmed this prediction. However, surface pressure distribution measurements on phantoms have shown only modest agreement with FEA simulations. Geometric uncertainties on the surface of the sensor as well as the variability of the absolute calibration make the array ill suited to measure accurate maps of the surface pressure distribution which might limit its utility for stress distribution measurements and elastic modulus reconstructions
Tuesday, January 29th, 2008
- R. G. Herb Condensed Matter Seminar
- Femtosecond Electron Diffraction:'Making the Molecular Movie'
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Dwayne Miller Chemistry and Physics University of Tornonto
- Abstract: Femtosecond Electron Diffraction harbours great potential for providing atomic resolution to structural changes as they occur, essentially watching atoms move in real time directly observe transition states. This experiment has been referred to as 'making the molecular movie' and has been previously discussed in the context of a classic gedanken experiment, outside the realm of direct observation. With the recent development of femtosecond electron pulses with sufficient number density to execute nearly single shot structure determinations, this experiment has been finally realized. A new concept in electron pulse generation was developed based on a solution to the N-body electron propagation problem involving up to 10,000 interacting electrons that has led to a new generation of extremely bright electron pulsed sources that minimizes space charge broadening effects. Previously thought intractable problems of determining t=0 and fully characterizing electron pulses on the femtosecond time scale have now been solved through the use of the laser pondermotive potential to provide a time dependent scattering source. Synchronization of electron probe and laser excitation pulses is now possible with an accuracy of 10 femtoseconds to follow even the fastest nuclear motions. The camera for the 'molecular movie' is now in hand. Atomic level views of the simplest possible structural transition, melting, have been obtained for a number of metals under strongly driven conditions (up to warm dense matter conditions) under which the dynamics occur over nm or molecular lengths scales. Direct observation of phonon distortions involved in electron-scattering and electronically driven structure changes in Si can now be resolved. Applications to specific molecular systems will also be discussed in the context of directly imaging reaction dynamics at the atomic level of inspection.
- Host: Eriksson
- Chaos & Complex Systems Seminar
- Cluster optimization in protein docking
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: Julie Mitchell, UW Department of Mathematics
- Abstract: Recent progress in obtaining docked protein complexes will be discussed. The combination of exhaustive search, clustering and localized global optimization can reliably find energy minima to highly nonconvex biomolecular energy functions. Using an energy function that adds desolvation and screened electrostatics to classical molecular mechanics potentials, the global minimum is found very near to the observed native state. This is demonstrated across a large number of benchmark examples.
Wednesday, January 30th, 2008
- No events scheduled
Thursday, January 31st, 2008
- R. G. Herb Condensed Matter Seminar
- Physics at the University of Nebraska-Lincoln
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Evgeny Tsymbal, Physics, University of Nebraska-Lincoln
- Host: Rzchowski
- Astronomy Colloquium
- Not Your Grandmother's HII Regions: An X-ray Tour of Massive Star- forming Regions
- Time: 12:00 pm
- Place: 6515 Sterling Hall (coffee at 11:30 am in 6521 Sterling)
- Speaker: Leisa Townsley, Penn State
- Abstract: The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We will tour several such regions, highlighting physical processes that characterize the life of a cluster of massive stars, from deeply- embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power great HII region complexes. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity or strong magnetic fields. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million- degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
Friday, February 1st, 2008
- No events scheduled