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Events on Thursday, May 8th, 2014

R. G. Herb Condensed Matter Seminar
On the way to understanding quantum matter: The death and rebirth of quasiparticles
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Peter Wolfle
Abstract: The low energy excitations of quantum matter generally have particle-like character. Their existence allows a relatively simple and economical description of thermodynamic and transport properties of condensed matter at low temperatures. However, the stability of these quasiparticles may be destroyed by fluctuations, e.g. at a classical or quantum phase transition into an ordered state. Inside the ordered phase the quasiparticles may be reborn in different form, together with other kinds of new quasiparticles. Examples are quantum phase transitions of metals into an antiferromagnetic or into a superconducting/superfluid state. Fluctuations may be also enhanced by dimensional reduction or by frustrating interactions, leading to the appearance of new types of quasiparticles. As examples one-dimensional quantum wires and the fractional quantum Hall effect will be considered,where “holons” and “spinons” , composite fermions and fractionally charged quasiparticles can be found
Host: Perkins
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Astronomy Colloquium
The Disks of the Milky Way Galaxy
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall
Speaker: Rosemary Wyse, The John Hopkins University
Abstract: I will discuss our current understanding of the disk(s) of the Milky Way. The vertical structure of stellar disks is determined by the relative importances of diverse physical processes, including gaseous dissipation prior to star formation, subsequent gas accretion into the disk, heating mechanisms such as interactions with transient spirals, and the mass ratios and gas content of merging systems. The radial structure reflects star-formation rates, angular momentum (re)distribution and interactions within the disk. The kinematic, chemical and age distributions of the stellar populations of present-day disks, as a function of scale-height and scale-length, provide further constraints on disk evolution. Decomposition of disks into distinct spatial components -- such as thin and thick -- is most meaningful when the spatial decomposition is accompanied by distinct stellar populations and/or different physical processes determining their properties. The most detailed information is available for stars in the Milky Way galaxy and I will demonstrate this decomposition based on recent results for the Milky Way disks.
Host: Prof John Gallagher
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