Physics Colloquium - Spring 2015

Speaker: Rajarshi Roy, Institute for Physical Science and Technology, Department of Physics and Institute for Research in Electronics and Applied Physics, University of Maryland

Abstract: The brain and eye function together to provide us information every day that we live. We will take a look at how this partnership works, and how we can learn about both vision and cognitive processing through optical illusions, as well as from the parts of the electromagnetic spectrum that are invisible to us. J. C. Bose was an experimental scientist who explored microwaves in the 1890s and then went on to investigate the electrophysiology of plants with table-top experimental apparatus designed and constructed with very limited means and a lot of imagination and persistence. We will examine his interdisciplinary endeavors and consider how such interests can be pursued today, beginning as math, science and engineering majors.

Speaker: Nick Pedatella, National Center for Atmospheric Research (NCAR)

Abstract: Sudden stratosphere warmings (SSWs) are associated with a rapid temperature increase in the wintertime polar stratosphere, as well as a deceleration, and potential reversal, of the normally eastward high latitude stratospheric winds. Perhaps surprisingly, although SSWs themselves are primarily a high latitude stratospheric phenomenon, recent results have demonstrated the global impact of SSWs on the middle and upper atmosphere. The variability in the middle and upper atmosphere can exceed 100%, and SSWs thus represent a significant source of upper atmosphere variability. Using numerical simulations from the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM) and Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) I will present recent results that demonstrate the mechanisms by which SSWs introduce variability into the middle and upper atmosphere, with a particular emphasis on the source of variability in the low latitude ionosphere. Results for both free-running (i.e., generic) and real SSW simulations will be presented. Current capabilities for simulating SSWs are also illustrated through comparing real SSW simulations with observations.

Speaker: Dirk Grupe, Department of Earth and Space Science, Morehead State University

Abstract: Gamma-Ray Bursts (GRBs) are the most energetic transient events in the Universe. Not only do they represent the violent end of a massive star and the birth of a black hole, but their explosions allows us to trace them throughout the entire Universe. With the launch of the NASA Swift Gamma-Ray Burst Explorer Mission our knowledge of GRBs has been revolutionized. With its fast slew capacity it is able to be on the position of a GRB within a minute or two after the GRB is detected, giving us access to the earliest phases of a GRB afterglow. Since its launch in November 2004, Swift has discovered more than 900 bursts, about 270 with spectroscopic redshift measurements - providing us the largest sample in history with prompt and afterglow observations. This unique sample enables us to perform unprecedented statistical studies of GRBs. In my talk I will review the history of GRB discoveries and their importance to astrophysics. I will present the Swift mission and explain what is unique and exciting about it and how Swift has given us new evidence for connections between the GRB prompt and afterglow emission. The fate of the burst is already determined during the explosion of the star. I will finish the talk by looking into the future and explain how we can use predictive data mining tools to determine the afterglow light curves and the redshifts of the bursts based on observed properties of the burst.

Speaker: David Weinberg, Department of Astronomy Ohio State University

Abstract: I will describe some of the scientific highlights from the Sloan Digital Sky Survey (SDSS), concentrating on those connected to cosmology and galaxy formation. In the three phases to date, SDSS-I, II, and III, the Sloan collaboration has carried out several of the largest and most ambitious surveys of the distant universe and the Milky Way galaxy, with deep digital imaging over one third of the sky and spectroscopy of more than 2 million galaxies, 200,000 quasars, and half a million stars. Cosmological achievements include: probing the epoch of reionization with the most distant known quasars; comprehensively characterizing the properties of galaxies and the relations between galaxies and their parent dark matter halos; discovering ubiquitous substructure in the outer Milky Way and more than a dozen new companion satellite galaxies; mapping cosmic expansion over the last four billion years with more than 500 Type Ia supernovae; and, through its precision measurements of structure on very large scales, providing a central pillar of the standard cosmological model based on inflation, cold dark matter, and dark energy. I will review these highlights, with particular attention to recent progress in measuring the properties of dark energy through baryon acoustic oscillations. I will summarize plans and prospects for SDSS-IV, which began in July 2014.