Spring 2008 Seminars
Seminars are held on Tuesdays, 3:45-4:45pm in SB110, unless otherwise noted. Meet at 3:30 in SB157 for refreshments (refreshments are available even on Tuesdays with no seminar!). See Calvin's Visitor Resources for maps and directions to the Science Building.
Tuesday, February 12 in SB110
| The Role of the Nucleus in Laser-Stimulated Double Ionization of Helium
||Students Zach Smith and John VanDyke with Prof Stan Haan|
Tuesday, February 26 in
|Tuesday, March 4 in SB110||Giant Magnetoresistance and the Nobel Proze||Prof. Steve Steenwyk|
|Tuesday, March 18 in SB110||Bulk, Thin film, and Computer Simulation Studies of Lipid Phase Transitions||Students Jess Vriesema and Josh Vanderhill|
|Tuesday April 1 in SB110||Forensic Characterization of Glass Fragments Using Particle Induced X- Ray Emission (PIXE) Spectrometry||Prof. Paul DeYoung
|Tuesday April 8 in SB110||The Nature of the Galactic Halo as Revealed by SDSS/SEGUE||Prof. Tim Beers
|Monday April 28||A Violent Side of the Universe||
Matie Hoffman, Boyden Observatory, South Africa
|Tuesday May 6 in SB110||
X-ray Measurements of the Eclipses of PPM 706067
|Student Jessie Taylor|
February 12: The Role of the Nucleus in Laser-Stimulated Double Ionization of Helium
Students Zach Smith and John VanDyke with Prof Stan Haan
This talk will give an overview and update on Prof Haan's NSF-funded research project regarding computer modeling of double ionization of atoms by lasers. The modeling is completely classical, but agrees well with experiment and allows for an analysis of the double-ionization process. It's now accepted that the primary mechanism of double ionization is recollision: one electron goes out from the atom, but the laser propels it back so that it smashes into the other electron and shares its energy. This talk will focus primarily on whether the nucleus plays any role in the recollision ionization process. Is it just a spectator, or can it influence the outcome of the collision?
February 26: Terrestrial meteorite impact geology – some background and a few case studies
John Weber, Assoc. Prof. Geology, GVSU
Geology has undergone a revolution in the past several decades. The Apollo lunar missions and an important discovery paper (Alvarez et al. 1980) have challenged us to think more realistically about the Earth’s place in the solar system. We now recognize meteorite impact as a fundamental process that shapes all planets, including our own. Surface weathering and plate tectonics tends to erase, bury, or destroy (subduct) craters on Earth. Nonetheless, about 150 terrestrial impact craters and potential impact craters have been identified (http://www.unb.ca/passc/ImpactDatabase/), many of which have been verified using well-established shock metamorphic criterion (French 1998). Prof. Weber will present some of this background, then share results from on-going research with GVSU undergraduate students on the Kentland crater (Indiana), Ries crater (Germany), and Eocene microtektites (Barbados).
March 4: Giant Magnetoresistance and the Nobel Prize
Professor Steven Steenwyk
Giant magnetoresistance (GMR) is a technologically important and physically fascinating phenomenon. Because it has opened whole new areas of investigation in the field of “solid state” physics and because it is has been exploited to generate billions of dollars of technology, its rather recent discovery and rapid technological application prompted the Nobel Committee to award the 2007 Nobel Prize in Physics to its discoverers, Albert Fert of France and Peter Gruenberg of Germany. You will learn (1) what magnetoresistance is, (2) what’s GIANT about GMR, (3) How devices are made to study and exploit it and (4) how it is used to make iPods possible. Professor Steenwyk has done research in this field, building GMR devices to illuminate new physics about how electrons carry “spin currents” inside conducting materials. In this work, done with collaborators at Michigan State University, he had opportunity to discuss his work with one of the Nobel laureates, Albert Fert.
March 18: Bulk, Thin film, and Computer Simulation Studies of Lipid Phase Transitions
Students Jess Vriesema and Josh Vanderhill
Lipids are the primary building blocks of cell membranes; understanding how these membranes open and close is of central importance in elucidating fundamental cell processes of fusion, division, viral infection, transport in and out of the cell (endocytosis and exocytosis), and even in the design of new anti-microbial peptides. We studied lipid phase transitions using laser-light scattering in bulk (mm thickness), thin film (µm thickness) and ultra-coarse grain computer simulations. We’ll discuss light scattering results for bulk systems of a lipid known as DEPE, preliminary thin film experiments, and pressure and temperature control in computer simulations.
April 1: Forensic Characterization of Glass Fragments Using Particle Induced X- Ray Emission (PIXE) Spectrometry
Paul A. DeYoung, Kenneth G. Herrick Professor of Physics, Hope College
A method has been developed to analyze the trace element concentrations in glass fragments using particle-induced x-ray emission spectrometry. This protocol gives a statistically meaningful determination of the possibility that two glass fragments originated from different sources. The application of such comparisons to forensic characterization of glass fragments is demonstrated for a test case. The sample preparation and analysis protocol will be described in addition to the statistical tests used in analysis. This approach has increased sensitivity over other x-ray fluorescence methods and has the advantage over inductively-coupled plasma spectrometry that it is entirely non-destructive.
April 8: The Nature of the Galactic Halo as Revealed by SDSS/SEGUE
Tim Beers, MSU
The outer region of the Milky Way, beyond the disk systems, has long been thought of as a single entity -- comprising old stars and globular clusters that represent the earliest populations of objects to have formed in our Galaxy. Previous studies of the halo have been limited by the small numbers of stars that could be confidently identified as members, and also by the lack of observed spectroscopy from which radial velocities and estimates of atmospheric parameters (such as temperature, surface gravity, and metallicity) could be obtained. Based on a very large set of new spectroscopy for stars in the halo of the Galaxy, obtained with the Sloan Digital Sky Survey, we show that the halo is clearly divisible into two broadly overlapping structural components. These are the inner halo, which is dominated by stars on highly eccentric orbits and exhibits a peak metallicity [Fe/H] = -1.6, as well as a somewhat flattened density distribution with a net prograde rotation, and the outer halo, which is dominated by stars on lower eccentricity orbits, exhibits a peak metallicity [Fe/H] = -2.2, and a spherical density distribution with a very high retrograde rotation. These results confirm expectations, based on the hierarchical Cold Dark Matter paradigm, that the outer halo of our Galaxy is likely to have been accreted from smaller sub-systems, perhaps similar to recently discovered low-luminosity dwarf spheroidal galaxies.
April 28: A Violent Side of the Universe
Matie Hoffman, Boyden Observatory, University of the Free State, South Africa
The development in recent decades of multiwavelength astronomy has opened new windows in our understanding of some of the most violent objects in the Universe: accretion disks, cataclysmic variable stars, micro-quasars and blazars. The presentation will introduce these topics and describe current research on them from the Boyden Observatory.