Department of Physics
SCHEDULED EVENTS (2005-06)
OTHER IMPORTANT DATES
Town Meeting of the Entire Physics Department
The purpose of this meeting is to discuss various matters of concern to students and faculty, e.g., colloquia, GRE, SPS, WOP, APS, LPW, Bjorklunden, letters of recommendation, the Senior Capstone program, ... All physics majors are expected to attend this meeting.
Mr. Paul Groszewski, Dual Degree Program representative from Washington University, St. Louis, MO, will be on campus to discuss Lawrence's affiliation with Washington University in a program that makes engineering available to Lawrence students. Individual appointments can be made with Professor Collett, Y-108. An open meeting at which Mr. Groszewski will discuss the affiliation and respond to questions will be held at 4:00 PM in Y-115.
Hyperfine Splittinge in Kr-83
Rupesh Silwal, LU, '06
Hyperfine splittings in the 4d-4, 4d-5, and 4d-1' states of KR-83 (I=9/2) have been measured using two-step laser excitation, and rf-discharge, and external cavity diode lasers. These are the first measurements of these particular hyperfine splittings. This talk will focus on work done in a research project supervised by Professor Brandenberger in the summer of 2005.
Analysis of a Possible Cooling Core Galaxy Cluster at z=1.03
Kyle Dolan, LU, '06
We present an analysis of Chandra observations of a massive cluster of galaxies at high redshift, Cl J1415+3612 at z=1.03, investigating whether the cluster possesses a cooling core. If the cluster does possess a cooling core, it will be the earliest known example of a massive cooling core cluster. We find Cl J1415+3612 to be of a relaxed morphology through the use of a two-dimensional X-ray surface brightness model, and we use spectral fitting to find that the temperature of the cluster is kT=(5.7+/-0.49) keV. Spectral fitting gives a temperature of (7.03+/-1.01) keV for the core and (4.45+/-0.58) keV for the outer cluster, which suggests that the core is warmer than the rest of the cluster, but too few counts are available for the spectral fits to be definitive. We find through one-dimensional spatial modeling that the radial surface brightness profile of the cluster cannot be satisfactorily modeled without some strong central peak in addition to the standard $\beta$ model, which is suggestive of the presence of a cooling core.
We find the total mass of the cluster to be (1.28+/-0.67)E15 time the mass of the sun, which indicates that it is one of the more massive known clusters. The bolometric luminosity of the cluster (within the defined spectral radius) was found to be L(r_s)=7.73E44 ergs/s.
The use of spectrally normalized exposure maps is also discussed, and we mention the importance of correcting for the degradation of the Chandra ACIS low-energy quantum efficiency when performing spectral fits to energies below 1 keV.
This talk will focus on work done in a research project conducted at the Institute for Astronomy, University of Hawaii at Manoa, in the summer of 2005.
Note that the morning part of the GRE examination is no longer given in paper format. It is available only at computer sites, the nearest two of which for Lawrence are in Oshkosh and Stevens Point. The examinations are administered at almost all times on a first-come first-served basis. If you are planning to take this examination this fall, you must register to reserve a time. October is a good month to take the general examination so that, come December (see later item), you can focus on the subject area examination, which is given as a paper and pencil examination. Further information about the GRE can be found at http://www.gre.org.
Th 13 Oct 4:15 PM Y-115: Physics Colloquium
Laboratory Dynamos: Exploring How Planets Generate Magnetic Fields
For many centuries the Earth's magnetic field was used for navigation and consequently it was measured extensively. Our understanding of its origin evolved a great deal over the past century. The first leap was the recognition that the field is generated within the Earth by a dynamo and is not primordial. Understanding the mechanism by which the liquid-metal core generates a magnetic field proved elusive, however, as anti-dynamo theorems eliminated axisymmetric models for the flow. The resulting theories depend upon a fully three-dimensional flow that breaks the symmetry of the system.
We have built a liquid-sodium experiment at the University of Wisconsin-Madison to study how turbulence can break the symmetry of a flow to produce a dynamo. I will explain the basic processes of magnetic field generation and share the initial results of the experiment.
Scanning Tunneling Spectroscopy of Single-Walled Carbon Nanotubes
Henry McNeil, LU, '06
In this era of increasing miniaturization, it is no surprise that nanoscience and nanotechnology are becoming increasingly important. Carbon nanotubes are one of the simplest and easiest to create nanoscale constructs, yet these tiny tubes possess many fascinating properties. With the aid of a scanning tunneling microscope, atomic resolution images of carbon nanotubes can be obtained. Through the use of scanning tunneling microscopy, Van Hove singularities can be observed in the local density of states in these tubes. This talk will focus on work done in a research project supervised by Professor Collett in the summer of 2005.
Diagnosing an Electron Plasma Trapped in a Toroidal
Magnetic Field by Observing How it Wiggles
Bao Ha, LU, '07
Traditional plasmas are notoriously difficult to confine. Electron plasmas consist only of freely moving electrons, are easier to confine, and exhibit many of the behaviors found in traditional plasmas. Requirements for confining electron plasmas in a toroidal magnetic field are addressed using the Lawrence Nonneutral Torus. The method of measuring confinement time destroys the confined plasma. During the confinement period, the plasma exhibits oscillations that, if left uncontrolled, grow and cause the plasma to scrape off against the trap walls. By applying the proper kick, an active feedback circuit can suppress the wiggle and improve confinement. When the feedback is modulated, the amplitude of the wiggle is allowed to grow and decay in discrete packets. The frequency of each of these packets is examined and a measurement of the trapped charge is extracted. This technique of measuring charge is quick and non-destructive. Higher magnetic fields and lower pressures resulted in confinement of up to 40~ms. This talk will focus on work done in a research project supervised by Professor Stoneking in the summer of 2005.
Use of Robotic Vehicles in Hydrographical Studies
Dan Casner, LU, '06
Autonomous underwater vehicles (AUVs) can be used to collect hydrographical data over much greater areas and spans of time than is practical using other techniques. However, implementation presents a variety of technological challenges. This talk provides a brief overview of some of the problems and solutions used by the Monterey Bay Aquarium Research Institute (MBARI) in their AUV program. A description of a research cruise using an AUV and data collected is also presented. Research for this project was performed during the summer of 2005 at MBARI.
Motion of Non-Uniform Strings
Claire Weiss, LU, '07, and Erik Garbacik, LU, '08
A well-known problem studied in physics is the motion of a string of uniform density, specifically the study of its normal modes of oscillation and its relative frequencies. What happens if the string does not have a uniform density? For example, a cello string that has varying density (either due to poor manufacturing, rosin build-up, or the elastic properties of the string) may vibrate differently than a uniform cello string, and the instrument could therefore sound quite different due to a shift in the positions of the higher harmonics. In this study, we explore solutions to the wave equation describing the motion of a string tied down at both ends for a uniform and a non-uniform string.
We employ two different numerical approximation methods. Both methods begin by dividing up the length of the string into small elements. Using the finite difference method and the computer program IDL (Interactive Data Language), we find the normal modes of a string whose density varies linearly from one end to the other end. Using the finite element method and the computer program MARC/Mentat, we find the normal modes of a string whose density changes abruptly at certain locations along the string and whose elasticity influences the tension.
When we set the density to be uniform along the string, our approximation methods yield results that agree with those known for a uniform string. When we set the density so that it varies along the string, we find that various properties of the solution change. For example, we find that as the string becomes denser, the speed of propagation of the wave slows down. We also find that the relative frequencies change (the frequencies are no longer multiples of the fundamental frequency), the wavelengths shorten, and the curvature increases. This talk will focus on work done in a research project supervised by Professor Cook in the summer of 2005.
SiC Coatings for SS 316 Corrosion Resistance
Annemarie Exarhos, LU, '07
A polymer based coating consisting of a PHMS (Poly(hydromethylsiloxane)) polymer matrix containing an inert SiC ceramic filler has been developed to retard the corrosion of a stainless steel alloy (SS 316) in oxidizing environments at processing temperatures from 800-1000 degrees-C. The effectiveness of the coating in slowing oxidation is examined through mass gain measurements by thermogravimetric analysis (TGA) and through oxide thickness measurements made from furnace processed samples in a scanning electron microscope (SEM). Reaction rate constants KP are determined from corresponding mass gain vs.~time and oxide thickness vs.~time plots. Determining the oxidation rates for each coating allows a model to be developed that describes the effectiveness of the PHMS + SiC coating for the corrosion resistance of SS 316 in oxidizing environments. Research for this project was performed during the summer of 2005 at Pacific Northwest National Laboratory and was supported by the Industrial Technologies Program of the US Department of Energy.
When antimatter attacks ...
Joan Marler, Fellow in Physics, Lawrence University
The title of this talk is the first line of a recent popular science article [E. S. Reich, New Scientist, 24 April 2004] highlighting research I was involved with at the University of California--San Diego. Seriously, there is no need for alarm, but recent progress in the ability to accummulate, cool, and manipulate anti-matter is leading to an increased presence of anti-matter particles in fundamental research and in applications. I will discuss UCSD's state-of-the-art scheme for positron (i.e., the anti-electron) trapping and beam formation. This technology has been exploited in low-energy atomic physics experiments at UCSD and for the formation of large numbers of anti-hydrogen atoms at CERN. Also, I will give an overview of new applications involving the positron in biophysics and condensed matter.
Physics Education Research at the University of Illinois
The Physics and History of Electron Microscopy and Microanalysis
Ellery Frahm, candidate for the PhD in physics at the University of
Minnesota
Blasting Stone Tools with Electron Beams: Crossroads of
Archealogy and the Natural Sciences
Ellery Frahm, candidate for the PhD in physics at the University of
Minnesota
Star in a Jar: An Introduction to Sonoluminescence
Nathaniel Douglas, LU, '06
Sonoluminescence---the production of light by sound---takes place when an air bubble in distilled and degassed water is trapped and driven ultrasonically. This talk on a capstone project supervised by Professor Brandenberger will describe the theoretical background of the phenomenon and the successful experimental creation of sonoluminescence at Lawrence during the fall of 2005.
Modeling of the m=1 Diocotron Motion in the Lawrence
Nonneutral Torus
Duncan Ryan, LU, '06
The primary diagnostic tool on the Lawrence Nonneutral Torus is monitoring the flow of image charges to and from wall probes. The m=1 diocotron mode of electron plasmas can be clearly seen using this method. While this motion can provide information about plasma density, it is not stable and ultimately results in the loss of electrons to the walls of the chamber. Active feedback allows this diagnostic technique to be used while maintaining trapped plasma. Using active feedback, pressure and magnetic strength scans were taken and results are reported.
The signal from the wall probes shows a distinct shape, which is dependent on several quantities of interest. Theoretical modeling using a cylindrical geometry was found to inadequately measure those quantities. Work is now being done numerically with the toroidal geometry to map the probe signal and determine the path of the plasma undergoing m=1 diocotron motions. This talk will focus on research during the summer of 2005 and a follow-up capstone project, both activities being supervised by Professor Stoneking.
Mo 10 Apr 4:15 PM Youngchild 115: Physics Colloquium
Heating the Solar Corona: A hot topic in plasma astrophysics
The surface or photosphere of the sun is a blackbody with a temperature of about 7500 deg-C, and the basic mechanism that heats the sun, nuclear fusion, is well understood. However, there is a disconcerting paradox: The temperature of the solar atmosphere or corona starts to rise away from the surface to about 1,000,000 deg-C. It's like walking away from a fire and you suddenly feel hotter. The energy that heats the corona is almost certainly stored in the magnetic field of the sun. There are two main competing models for how this energy is released: 1) Magnetic waves and 2) Tearing and reconnection of the magnetic field. Both models are probably valid in different regimes. In this talk, I will present an overview of the coronal heating paradox and the two heating models. Then I'll talk about current research by plasma physicists, using both remote observations and laboratory simulations, focused on substantiating these models.
Fr 5 May, 2:00-4:30 PM, Physics Floor, Youngchild Hall: Departmental Open House.
Sa 6 May, 1:00-5:00 PM, Youngchild Hall: Alumni Physics Symposium. Speakers at the symposium will be
Mo 15 May 8:00 PM Youngchild 121: Science Hall Colloquium
Cosmic Evolution: From Big Bang to Biology
See how the universe turned from an ultra-dense iota of mass and energy in the big bang to a region 30 billion light years across containing 50 billion galaxies. Along the way, the story of the elements will be told, the essential prelude to planets and life.
Tu 16 May 11:10 AM Youngchild 115: Physics Colloquium
Probing Dark Energy with Quasars
The largest component of the universe is dark energy, the existence of which is indicated by using supernovae as standard light bulbs to trace the changing rate of expension. A completely independent test of dark energy is described, based on using distant quasars to illuminate parallel paths through the diffuse intergalactic medium.
Mo 22 May 8:00 PM Youngchild 121: Phi Beta Kappa Lecture
High Temperature Superconductors: From Broken Symmetries to Cell Phones
Superconductivity, observed in many metals when cooled to extremely low temperatures, was discovered in 1911. In 1986, materials were discovered that superconduct at much more easily obtainable temperatures. This discovery motivated an unprecedented world-wide flurry of research: Not only are applications promising, but these high-temperature superconductors represent a new solid state of matter that break certain fundamental symmetries of Nature.
Tu 23 May 11:10 AM Youngchild 115: Physics Colloquium
High-Temperature Superconductors: Playgrounds for Broken Symmetries
Studies of symmetries and the consequences of breaking them have led to deeper understanding in many areas of science. The high-temperature superconductors, discovered in 1986, motivated an unprecedented world-wide flurry of research, not only because applications are promising, but also because they represent a new state of matter that breaks certain fundamental symmetries. After providing a general background on broken symmetries and superconductivity, we show how planar tunneling spectroscopy can detect the broken symmetries of gauge (superconductivity), reflection (d-wave superconducting order parameter) and time-reversal (ferromagnetism).
Photo Shoot: 4:15 PM (promptly) on the steps on the west side of Downer Commons. Faculty members, seniors and juniors leaving for engineering schools should meet on the steps for the taking of this traditional photo.
Modeling the m=1 Diocotron Mode in the Lawrence Nonneutral Torus
Annual Reception for physics graduates and their graduation guests.