Events at Physics |
Events During the Week of February 24th through March 2nd, 2008
Monday, February 25th, 2008
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Magnetic Fields in HIgh Intensity-Laser Produced Plasmas
- Time: 12:05 pm
- Place: 2241 Chamberlin Hall
- Speaker: Karl Krushelnick, University of Michigan
Tuesday, February 26th, 2008
- Chaos & Complex Systems Seminar
- Generalising the Reynolds number from turbulence to sand-piles(S.O.C.) to ecosystems
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: George Rowlands, University of Warwick
- Abstract: Some concepts such as scaling and universality common in the study of fluid turbulence are applied to self-organized criticality and simple predator-prey models more common in the biological field. The common thread is a generalisation of the Reynolds number.
- Astronomy Colloquium
- The Stellar Populations of the Andromeda Spiral Galaxy
- Time: 3:45 pm
- Place: 6515 Sterling Hall (coffee at 3:30 pm in 6521 Sterling)
- Speaker: Jason Kalirai, University of California - Santa Cruz
- Abstract: Simulations of hierarchical galaxy formation suggest that large galaxies such as the Milky Way and Andromeda (M31) should contain extended stellar halos that are chemically distinct (more metal poor) from the inner spheroid. Yet, no such population has been discovered in our nearest neighbor, M31. We report on the first results from a photometric and spectroscopic survey of red giant branch (RGB) stars over a large expanse in M31. Using a new technique based on photometric and spectroscopic diagnostics, we are able to isolate bonafide M31 RGB stars out to a distance five times further than previous studies (165 kpc). In addition to the kinematically cold disk and metal-rich inner spheroid, we find clear evidence for an extended, power law halo component in M31. The spectroscopic and photometric metallicity of this new population is measured independently and found to be metal-poor, [Fe/H] = -1.5. We also present the discovery of a new dwarf spheroidal galaxy in M31 and evidence for spatial and kinematical substructure in the halo. The discovery of this stellar halo puts to rest much of the disparity that has existed between the Milky Way and M31 halos, and brings forth an ideal testbed for detailed simulations of galaxy formation.
Wednesday, February 27th, 2008
- No events scheduled
Thursday, February 28th, 2008
- String Theory Seminar
- Title to be announced
- Time: 2:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Yu Nakayama, Berkeley
- Astronomy Colloquium
- Dark Matter in Dwarf Galaxies
- Time: 3:30 pm
- Place: Room TBA
- Speaker: Josh Simon, CALTECH
- Abstract: Over the last several years, three crucial shortcomings of the Cold Dark Matter (CDM) model have been discovered on galaxy-size scales. I present new observations addressing two of these problems: the missing satellite problem and the central density problem. I describe results from a Keck spectroscopic survey of the ultra-faint dwarf galaxies orbiting the Milky Way that were recently discovered by the Sloan Digital Sky Survey. We measure the masses of these galaxies based on their stellar kinematics and investigate whether they can account for the missing CDM satellites. I also present a rotation curve analysis of eight nearby low mass disk galaxies, based on high-resolution 2D velocity fields in Halpha and CO. This observing program has been designed to overcome some of the limitations of other rotation curve studies that rely mostly on long-slit spectra or low-resolution HI observations. We find that these objects exhibit the full range of dark matter density profiles between constant density and NFW halos, in contrast to the single universal density profile seen in CDM simulations. We consider possible explanations for the differences between observed and expected density profiles and argue that they are consistent with being caused by halo triaxiality.
- Special Plasma Physics Seminar
- Testing Gyrokinetic Turbulence Simulations
- Time: 4:00 pm
- Place: 5280 Chamberlin Hall
- Speaker: Dr. Robert Budny, Princeton Plasma Physics Laboratory
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.