Events at Physics

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Events on Tuesday, April 13th, 2010

Chaos & Complex Systems Seminar
Shock Waves in Nature and in Numerical Computations
Time: 12:05 pm
Place: 4274 Chamberlin Hall
Speaker: James Rossmanith, UW-Madison, Dept. of Mathematics
Abstract: Shock waves are propagating disturbances that are characterized by an abrupt, nearly discontinuous change in the characteristics of a fluid or plasma. They can occur in a variety of phenomena in both laboratory and natural settings. Mathematically, shock waves are difficult to handle since in general they are not unique solutions of the equations that model them. Computationally, shock waves are difficult to handle for several reasons: (1) most discontinuous cannot be exactly represented on a discrete mesh, (2) standard high-order methods are unstable for shocks, and (3) the numerical schemes must be carefully constructed to yield the physically correct solution.

In this talk I will begin by briefly reviewing the basic theory of shock waves. I will then, mostly through computational examples, describe the various pitfalls in trying to numerically solve equations with shock solutions. Finally, I will describe some strategies based on adaptive mesh refinement to obtain highly accurate numerical solutions.

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Astronomy Colloquium
Nearby, Thermally Emitting Neutron Stars
Time: 3:30 pm - 5:00 pm
Place: 3425 Sterling Hall
Speaker: David Kaplan, UW-Milwaukee
Abstract: Neutron stars are among the densest objects in the universe. The conditions in their centers are largely unconstrained by current theoretical physics or terrestrial laboratories, leaving a wide variety of compositions and structures possible. Observations of thermal emission from neutron stars -- specifically measurements of their sizes and cooling rates -- may therefore be the best way to constrain the behavior of matter in these extreme conditions. I will discuss a sample of nearby, cooling neutron stars that we are using for this purpose. We are attempting to pin down the basic parameters of these neutron stars with a variety of ground- and space-base observations, coupled with theoretical modeling. Along the way, we have encountered a number of interesting astrophysical puzzles that I will describe.
Host: Astro Dept
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