Events at Physics |
Events on Friday, February 29th, 2008
- Physics Department Colloquium
- Topological defects in nanomagnets
- Time: 1:20 pm
- Place: 2241 Chamberlin Hall (coffee at 1:00)
- Speaker: Oleg Tchernyshyov, Johns Hopkins University
- Abstract: Formation of magnetic domains in a macroscopic ferromagnet is a familiar phenomenon caused by a competition between local and long-range forces. The physics of domains becomes drastically different in nanosized magnets. In particular, domain walls in magnetic nanowires are composite objects containing a few elementary topological defects: vortices with integer and fractional winding numbers. Dynamics of such domain walls can be reduced to the motion of these "elementary particles". A nonzero skyrmion charge of a vortex strongly influences the dynamics of composite domain walls.
- Host: Chubukov
- Physics Department Colloquium
- Probing the sources of solar magnetism with helioseismology and simulations
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Juri Toomre, JILA and Dept Astrophysical & Planetary Sciences, University of Colorado
- Abstract: There exist major challenges to understand how the Sun builds the large-scale and intense magnetic fields that we observe at its surface and how these fields evolve in time. The origin of these magnetic fields must rest with dynamo processes occurring deep within the star. Many complex dynamical elements are involved in the operation of the solar global dynamo. These include the differential rotation of the convection zone and the tachocline at its base, turbulent production and transport of the magnetic fields by the convection, shear amplification of the fields, and magnetic buoyancy that leads to the eventual field eruption onto the photosphere. Major advances in supercomputing are allowing us to improve the fidelity with which we can model these intensely turbulent processes. These efforts are aided by continuing guidance provided by helioseismology in probing dynamics in the solar interior. We discuss the close interplay between helioseismology and recent 3-D simulations in studying the solar global dynamo.