Events - Daily
November 29, 2012 >>
|Thursday, November 29|
Condensed Matter Seminar - Tomasz Durakiewicz, Los Alamos National Laboratory - Time-resolved ARPES of f-electron systems
The coherence temperature, T*, sets an important energy scale in correlated f-electron systems. In this scale the hybridization gap opens at or in the vicinity of the Fermi level and the gap magnitude scales with effective quasiparticle mass. The coherent part of the self-energy corresponding to the gap formation is reduced at high temperatures, and the incoherent part corresponds to quasiparticle scattering. The coherent term in the self-energy expresses the mixing of f and d bands and is directly responsible for repulsion, producing the hybridization gap. In this talk I will show examples of time-resolved ARPES measurements of f-electron systems, providing valuable information about the evolution of coherence and the dynamics of the related quasiparticle states.
Jadwin 475 · 2:00 p.m.– 3:30 p.m.
Physics Colloquium - Elizabeth Olson, Columbia University - "Amplification of Sound in the Mammalian Cochlea"
The snail-shaped mammalian cochlea houses a narrow strip of sensory tissue that separates compartments of salty water. Sound stimulation launches a mechanical traveling wave down the cochlea that peaks in a tonotopic manner: high/low frequencies peak in the cochlear base/apex. Sensory hair cells respond to the motion with intracellular current and voltage. In outer hair cells the electrical response elicits mechanical forces, by means of piezoelectric prestin proteins in the cell membrane. These forces augment the motion of the sensory tissue, boosting and sharpening the mildly frequency-resolved pattern of motion that obtains in the passive (dead) cochlea. The motion is increased by a factor of 100 or more for low sound pressure level sounds and very little for high level sounds, thus active cochlear mechanics is compressively nonlinear. Our work explores the dynamics of cochlear amplification in-vivo, using micro-pressure and voltage sensors and laser interferometry. Our recent results detect power amplification in the cochlea and inform the mechanism that gives rise to the localized sharpening of cochlear responses that is fundamental to normal hearing.
Jadwin A10 · 4:30 p.m.– 5:30 p.m.