Department of Physics
SCHEDULED EVENTS (2008-09)
OTHER IMPORTANT DATES
Note that what used to be the morning part of the GRE examination (the general part) 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.
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.
A Homebuilt Total Internal Reflection Flourescence Microscope Images Biological Motor Protein
Kinesin
David Meichle, LU '09
Many interesting cellular processes are unobservable with traditional optical microscopy, which is diffraction-limited to hundreds of nanometers. We are specifically interested in nanometer scale dynamics of the kinesin molecule, a motor protein responsible for transporting a variety of cellular cargo. This is accomplished by single molecule fluorescence microscopy, where a single fluorescing molecule (quantum dot) is attached to a sample. A CCD camera images the quantum dot with a total internal reflection fluorescence (TIRF) microscope. These images appear as single diffraction limited spots of radius ~250 nm. Observations in the unresolvable nanometer scale become a matter of precisely localizing the quantum dot, by finding the center of the diffraction spot. This summer we successfully constructed a TIRF microscope from scratch. To localize the quantum dots and track the sample, we wrote a robust software package which performs non-linear least squares fitting. Characterization of the microscope and analysis software has shown localization precision of <3nm at a 30 Hz frame rate. Further work is needed to improve the precision to our target frame rate of 1kHz. This microscope recently imaged walking kinesin, and awaits further use in other experiments. This talk will report on work supervised by Professor Douglas Martin during the summer of 2008.
Measuring Fire with a Laser:
Absorption Spectroscopy Measuring Concentrations and Temperatures of Gas Molecules in Flames
Robert Niederriter, LU '10
Computer flame models require data about gas molecule concentrations and temperatures to create more accurate simulations. Absorption spectroscopy measurements using tunable diode lasers have produced fast results, but lack sensitivity. Cavity Enhanced Absorption Spectroscopy (CEAS) and Cavity Ring-down Absorption Spectroscopy (CRAS) have been developed to allow higher sensitivity in flame measurements. CEAS uses a high number of passes (~1000) through the gas sample to greatly increase the absorption path length and thus the precision of the absorption measurement. CRAS provides greatly superior sensitivity by using many reflections and measuring ring-down time rather than the ratio of light intensities. High precision measurements have been made using CEAS of absolute concentrations of atmospheric methane. The same techniques can soon be used in measuring flames. This talk will report on work done during the summer of 2008 at the Physical Chemistry Institute of the Heidelberg University in Germany.
Football Physics
Timothy Gay, Professor of Physics, University of Nebraska
Professor Timothy Gay will discuss his recent series of one-minute physics lectures delivered to the 80,000 fans that regularly attend the University of Nebraska football games. The topics of these mini-lectures range from gyroscopic motion to ionizing collisions between linebackers and running backs. The problem of simultaneous edification and amusement of the fans in the stands is considered. Gay's work has been featured on ABC World News Tonight with Peter Jennings, ESPN's Cold Pizza, and front page stories in the Wall Street Journal, and the Tuesday Science section of the New York Times, as well as in People Magazine, ESPN Magazine, the Boston Globe, the Washington Post, and a variety of other television and radio outlets. Gay has also written a book, Football Physics, published by Rodale. It recently came out in a second edition retitled The Physics of Football published by Harper-Collins Paperbacks. Its target audience is high school stuents and football fans of all ages.
Understanding Parametric Instability in Advanced LIGO Fabry-Perot Cavities
Daniel Fulton, LU '09
We address the problem of parametric instability (PI) in a Fabry-Perot cavity with Advanced LIGO parameters. Three treatments of PI in gravitational wave interferometers exist: (1) approximation of the optical cavity as a linear feedback system on test mass vibrations, (2) examination of the rate of work done on the test mass versus natural power dissipation, and (3) Lagrangian analysis of eigenfrequencies in the coupled cavity-test mass system. All three approaches assume time static parameters. First, we develop approach (1), and then illustrate its equivalence with (2) and (3). Using (1), some time dependent parameters in PI may be evaluated. Specifically, we consider drift in the resonant frequency of the cavity test mass and the ability of this drift to inhibit PI build up.
Measurement of Plasma Flow and Temperature
Gennady Fiksel, University of Wisconsin - Madison
How does one measure the velocity of a remote object? One example is a radar gun, used to catch speeders and to clock the baseball pitch velocity. The gun shines a radio wave towards the object and measures a small change in the frequency of the reflected wave. The change in the wave frequency is proportional to the wave velocity - the famous Doppler effect. A similar approach is used to measure the velocity and the temperature of plasma electrons and ions. Instead of radio waves, though, intense light beams created by lasers and intense particle beams created by particle beam injectors are used. I will discuss applications of these approaches and challenges that need to be overcome.
EIT with Noisy Lasers
Mackenzie Van Camp,. LU '09
Electromagnetically induced transparency (EIT) is a powerful tool for manipulating and storing the information carried in a light pulse. EIT, however, is fragile: it is achieved by creating a coherent superposition of ground states in an atomic sample, and any process which disrupts that coherence can quickly degrade the EIT, and with it the ability of the atoms to store information. This talk describes my progress towards quantifying the effects of radiation trapping, a source of decoherence in high-density EIT media. My experiment uses laser frequency noise to observe changes in the coherence lifetime at different densities and laser powers. My goal is to quantify the relationship between radiation trapping and coherence lifetimes, a result which will have practical applications in the fields of quantum memory, quantum computing, and nonlinear optics. I will report on my initial characterization of noise spectroscopy at the Harvard-Smithsonian Astrophysical Observatory during the summer of 2008, and my efforts to recreate and expand upon the experiment as my Capstone Project here at Lawrence. The work at Lawrence was supervised by Professor Shannon O'Leary.
Controlling magnetization dynamics in ferromagnetic nanowires
Andrew Kunz, Marquette University
Magnetic nanowires have been proposed as an alternative for future generations of recording, sensing, and logic devices. The viability of these potential devices depends on the ability to quickly inject, move and control the magnetic domain walls which carry the information. A physical understanding of how a magnetic moment responds to an interaction is necessary to reliably overcome barriers to controllable motion. I will present my groups results showing how to inject and move single domain walls and how the "nano" properties of these wires had led to a new method for manipulating multiple walls necessary for functioning devices.
Memory as vibration in a disconnecting air bubble
Wendy Zhang, University of Chicago
The disconnection of an underwater bubble provides a simple example of competition between asymmetry and focusing. Focusing a finite amount of energy dynamically into a vanishingly small amount of material requires that the initial condition be perfectly symmetric. In reality, imperfections are always present and cut off the approach towards the focusing singularity. We use a combination of theory, simulation, and experiments to show that the dynamics near disconnection contradicts the prevailing view that the disconnection dynamics converges towards a universal, cylindrically-symmetric singularity Instead an initial asymmetry in the shape of the bubble neck excites vibrations that persist until disconnection. We argue that such memory-encoding vibrations may arise whenever the formation of the singularity involves a focusing of materials.
The Power of Diffusion Nuclear Magnetic Resonance
Michelle Milne, LU '04, Washington University
Nuclear Magnetic Resonance (NMR) is a powerful technique that has been used by a number of fields, from physics to chemistry and medicine. In particular, my research has used Diffusion NMR to study disease progression in emphysema and to help develop diagnostic and treatment procedures. During this talk, I will give a basic understanding of how NMR works and show a few examples of how it is used in lung imaging.
Photo Shoot: 4:15 PM (promptly) on or near the front steps of Downer Commons. Faculty members, seniors, and juniors leaving for engineering schools should meet in the courtyard for the taking of this traditional photo.
Polarizing Ideas: How to Create Controversy
David Harbage, LU '09
This talk will report on a senior capstone project supervised by Professor Douglas Martin.
Diocotron Modes: Making the World a Better Place
Jason Smoniewski, LU '09
This talk will report on a senior capstone project supervised by Professor Matthew Stoneking.
Critical Scattering and Phase Transitions in Liquid Crystals
Andrew Phillippi, LU '09
This talk will report on a senior capstone project supervised by Professor Jeffrey Collett.
Annual Reception for physics graduates and their graduation guests. All those associated with the Department of Physics who happen to be in Appleton are invited.
Gathering for all physics majors and minors returning from reunion, providing an opportunity for those individuals to meet and greet both current and retired faculty members, learn of new initiatives in the Department, network with one another, and bring all attending up to date on their activities since graduation.