Seminar: Spring 2005

Seminars are held on Tuesdays, 3:45-4:45pm in SB-110, unless otherwise noted. Meet at 3:30 in SB-157 for refreshments (refreshments are available even on Tuesdays with no seminar!). See Calvin's Visitor Resources for maps and directions to the Science Building.

Schedules from previous semesters: Fall 2004, Spring 2004, Fall 2003, Spring 2003, Fall 2002, Spring 2002, Fall 2001, Spring 2001, Fall 2000, Spring 2000, Fall 1999.

February 8 : Wide Bandgap Semiconductors: The Challenge of High Temperature Devices.
       Ruby N. Ghosh, Research Associate Professor, Dept. of Physics, Center for Sensor Materials, Michigan State University.
       Devices based on the wide bandgap semiconductor (3 eV) silicon carbide, are well suited for operation at elevated temperatures. Examples include gas sensors and electronic circuits for control and emissions applications in automobiles and power plants. In the first half of my talk I will introduce the materials, chemical and electronic properties of SiC, followed by the physics of field-effect devices. I will then describe our work in developing a high temperature SiC based chemical sensor for detecting hydrogen containing species in exhaust gases.

February 15: On the road to new semiconducting materials: carrier transport in amorphous nitride semiconductors
       Prof. Mark Little, Physics Department, Hope College.
New material advances have brought about huge changes in technology and our everyday life. Short wavelength lasers, used in ever larger optical data storage drives, are one example. An area of current research is in amorphous and nanocrystalline nitride based materials. In my research, I am investigating the charge carrier transport properties which currently limit the usefulness of these materials. Good charge transport is needed for these materials to be used in dc electrical circuits. By investigating the carrier mobility and diffusion as it relates to material growth parameters, the hope is to find new useful materials for technology and to add to the fundamental knowledge of carrier transport in the amorphous/nanocrystalline regime. I will outline some of the fundamental questions my group is trying to answer, give an overview of the techniques used, and discuss some early results.

February 22: Hysteresis Measurements of Lipid-Water Systems via Laser Light Scattering
       Alexis Reynolds and Peter Cook, Calvin College.
Lipids are important biological molecules which can exist in different phases. While the phases themselves are well studied, the phase changes are quite poorly documented, given the hysteresis of these transitions. Laser light scattering provides a new way of accurately measuring where these phase transitions occur.

March 1: An Exploration of Lipid-Water Systems: Utilizing Computer Simulation, Calorimetry and Capacitance
       Mitch Machiela, Dan Russcher and Professor Paul Harper, Calvin College.
Lipids are important biological molecules that undergo various phase transitions. There are many techniques that can be taken in the study of lipid-water phase transitions. This seminar will discuss how computer simulations, differential scanning calorimetry and capacitance measurements have helped enhance our understanding of the inverted hexagonal-lamellar phase transition in lipid-water systems.

March 22: Gravitational Lenses, Dark Matter, and Radio Galaxies
       Professor Deborah Haarsma, Calvin College.
Gravitational lenses are one of the most beautiful confirmations of Einstein's theory of general relativity. A massive galaxy curves spacetime and acts as a lens to light from distant objects behind it. By studying the distorted light, it is possible to deduce the amount and distribution of dark matter in the galaxy. Over the last few years I have worked with Calvin students and off-campus collaborators to search for radio galaxies which are gravitationally lensed, using the Very Large Array (VLA) radio telescope, the Hubble Space Telescope, and other instruments. I will report on the results of our survey and the discovery of a likely gravitational lens.

March 29: Applied Physics in the Chemical Industry
       Dr. Udo Pernisz, Thin Film Technology Platform, Advanced Technologies and Ventures Business, Dow Corning Corporation.
       In a personal account of the experience of an experimental condensed matter physicist working in the Specialty Chemicals Industry, several examples of projects and typical tasks are presented with some technical detail. This overview demonstrates the wide range of industrial R&D activities, from establishing the capability of characterizing electronic thin films, to studying the drainage mechanism and effect of surfactants in the manufacture of polyurethane foams, to discovering photonic properties of silicon-containing compounds. Some general observations on the requirements for a successful industrial career, and how all this versatility eventually leads to commercial products, will conclude the presentation.

April 5: Imaging the Saturn System: Polarization and More
       Elise Crull and Professor Larry Molnar, Calvin College.
A year ago, we we made a sharper image of Saturn at radio wavelengths, finding new structure both in the rings and on the planet itself. Radio emission from the rings is largely scattered light, and its properties are determined in part by the spatial distribution of the trillions of particles composing the rings. Since then, we have extended this work to look at the polarization characteristics of the radio emission. We will show how results of numerical simulations of light scattering through the rings and compare them with the images. We will also compare what we have found to recent images at very different wavelengths made with the Keck and Hubble telescopes.

April 12: Double Ionization of Helium by High-Intensity Lasers -- A Completely Classical Description
       Llian Breen and Professor Stan Haan, Calvin College.
The goal of our research has been to explain how a high-intensity laser can strip both electrons from a helium atom. Experiments around the world have shown that the amount of double ionization is up to a million times greater than would be expected if the electrons behaved independently from each other. Theoretical work has indicated that the most likely mechanism is "recollision," a process in which one electron escapes but then is pushed around by the external laser field so as to return to the core area and share energy with the inner electron. We have been investigating whether the double ionization can be explained using only classical mechanics, or whether quantum mechanics will be necessary. We start out by using a classical ensemble that is meant to mimic the quantum ground state. Each ensemble consists of 100,000 to 500,000 classical atoms, each of which has two electrons bound by electrical forces to the vicinity of a nucleus. Each atom in the ensemble has energy equal to the ground state of the helium atom, but the electrons of each classical atom have slightly different positions and momenta. We use a computer to propagate each model atom through a 10-cycle intense laser pulse. We then analyze the final positions and momenta of the electrons and compare with experiment. We find that our procedure qualitatively reproduces all the experimental results. Finally, we examine the mechanism of double ionization by
analyzing the time development of individual atoms that doubly ionized.

April 19: Einstein on Tiny Spheres in a Fluid: Establishing the Reality of Atoms and the Validity of Statistical Physics — a look at two of Einstein’s less famous papers of 1905.
       Professor Steve Steenwyk, Calvin College.
This is the first of a number of events to resume in the fall in which the Department of Physics and Astronomy will seek to commemorate the achievements and consequences of Einstein’s miraculous year, 1905 as part of our celebration of The International Year of Physics in 2005.
       In his Ph.D. dissertation of 1905, Einstein used classical hydrodynamics to analyze the effect of small spheres (down to molecular size) on friction in a fluid and, by this means, showed a way to determine sizes of molecules. Similarly, in his seminal 1905 paper on Browning motion of tiny spheres, he again showed the way to use these motions to experimentally validate Maxwell’s and Boltzmann’s work on the statistical behavior of atoms in thermal motion. Prior to this, many influential philosophers and scientists resisted the atomic view and associated statistical approaches despite the successes of Maxwell and Boltzmann in accounting for the behavior of gases and other phenomena using such methods. (Thermodynamics, electrodynamics and Newtonian mechanics required no reference to atoms.) It was characteristic of Einstein to choose to solve just those problems that could bring clarity to the vexing dilemmas that were confronting existing theories when applied to the realm of the atom. Thus, he made an essential contribution to finishing the foundation for the many developments that continue to flow from the broad field now called “statistical mechanics.” In that year he also published his paradigm changing work in the theory of special relativity, the formula E=mc2, and in the quantization of light to explain the photoelectric effect as an essential step toward the 20th century’s greatest conceptual revolution, quantum mechanics.

May 3 :
       Part 1: The Ultimate Strategic Defense Initiative: Computing Asteroid Orbits for Fun and Self-Preservation
       Matt Voorman and Prof. Larry Molnar, Calvin College.
Of all the types of celestial bodies one might study, asteroids are the one that has much more than academic interest, in that they occasionally and catastrophically collide with Earth. As Calvin students have begun to make a (modest) contribution to the cataloging of asteroids (with 32 new discoveries to date), we have a need for computing the future trajectories of these objects. In this seminar we will present a flexible and understandable orbit calculator developed using Mathematica and demonstrate its use interpreting data on some recent discoveries.
      Part 2: Faraday Rotation: Interactions of Atoms, Light, and Magnetic Fields
       Lee Miller and Prof. Matt Walhout, Calvin College.
Since a discovery by Michael Faraday in 1845, it's been known that magnetism affects light. During the summer of 2003, professor David VanBaak and students Chris Walker and John VanderWeide set up the Faraday rotation experiment, recorded data for the Rubidium 85 and 87 isotopes, and fit models to the data. Further research was done last summer to model the data in order to confirm and explain the results of the experiment quantum mechanically. This seminar provides an overview of the experiment, and presents the methods and results of the new theoretical studies.

May 10: Trapping Krypton-84 Kr and Krypton-83
       Shannon Fogwell and Professor Matt Walhout, Calvin College.
Magneto-optical traps are useful for measuring various properties of atoms, including the lifetimes of metastable states. For example, in the trap here at Calvin, the lifetime of the 3-P_2 state of Krypton-84 has been measured to be 28 seconds. In the future, we would like to compare this measurement with a similar one in Krypton-83 and to study the destabilizing effect of nuclear spin. Last summer, work was done on an absorption imaging system to improve measurement capabilities. This semester, further work was done on laser diagnostics and redesigning the laser setup to allow trapping of both Krypton-84 and Krypton-83.