Events at Physics |
Events on Thursday, May 7th, 2009
- R. G. Herb Condensed Matter Seminar
- Let there be light: from graphene oxide to dark excitons
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Jay Kikkawa, University of Pennsylvania
- Abstract: TBA
- Host: Robert Joynt
- Atomic Physics Seminar-Note special time
- Schlieren measurements of Hg density gradients in an ultra-high pressure arc lamp
- Time: 12:30 pm
- Place: 5310 Chamberlin
- Speaker: Joe Kane, University of Wisconsin-Madison
- Abstract: A Brewster angle reflection measurement is used to determine the Hg vapor density at the arc tube wall of an ultra-high pressure lamp. The density measurement in combination with the wall temperature yields a pressure of 201 +/- 11 bar. This lamp pressure in combination with an arc core temperature measurement yields an arc core Hg vapor density of 1.78 x 10^20 cm^-3, which agrees with the density from resonance collisional line broadening measurements of the 1014 nm Hg line. These density results are combined with Abel inverted laser deflection or schlieren measurements to determine a density/temperature map of the Hg vapor in the lamp. The laser deflection technique is sensitive in the arc core and mantle, unlike emission techniques which are sensitive only in the arc core.
- Host: Jim Lawler
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- High Precision Cosmology with Baryon Acoustic Oscillations
- Time: 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Hee-Jong Seo, Fermilab and U. Arizona
- Abstract: Baryon acoustic oscillations (BAO) in large galaxy surveys can provide an excellent standard ruler test to measure the cosmological distance scale, such as the angular diameter distance and the Hubble parameter, and therefore dark energy properties. This requires that we understand all of the physical effects that could alter the acoustic feature during the nonlinear evolution of structure. There are two important aspects of the nonlinear effects on BAO. First, the BAO signature is gradually reduced with time and in scale due to nonlinear growth of density fields, redshift distortions, and galaxy bias. Second, the various nonlinear effects may alter the observed BAO scale at low redshift, relative to the linear acoustic scale derived from the CMB, which would result in biased estimation of dark energy parameters. In this talk, I will present effects of such nonlinearities on BAO from N-body results: nonlinear growth and redshift distortions degrade the contrast of BAO while shifting BAO less than ~0.5% at z=0.3. I will show that most of these nonlinear effects can be reversed by a simple reconstruction scheme.I will also discuss the effect of galaxy bias on BAO.
- Host: Peter Timbie