Keith Morris, graduate student at Tech, will present the Physics Department seminar. He will discuss, "The VLA Atmospheric Phase Interferometer." The Atmospheric Phase Interferometer (API) is a two-element atmospheric seeing monitor that measures turbulent refractive index variation through the atmosphere by examining phase differences in a satellite beacon signal detected at two (or more) antennas. With this measurement, the VLA scheduling software is able to consider atmospheric stability when determining which frequency observation to schedule next. Morris will present some statistical properties of turbulence, the effects of atmospheric stability on radio interferometric observations, and discuss details of the instrument and the data that it collects. 4 p.m. in Workman 101.