Department of Physics
SCHEDULED EVENTS (2004-05)
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.
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.
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.
Th 14 Oct 4:15 PM Y-121: Science Hall Colloquium
Stone Cold Science: Things Get Weird Around Absolute Zero!
As things get colder and colder, they move slower and slower, and they get weirder and weirder. At absolute zero, they become absolutely weird. Albert Einstein predicted that, when atoms get cold enough. they undergo a sort of quantum identity crisis. This effect is now known as Bode-Einstein condensation. Dr. Cornell will explain how scientists reach the necessary record-low temperatures and explain why one goes to all the trouble to make this bizarre state of matter.
Fr 15 Oct 11:10 AM Y-115: Physics Colloquium
Rotating the Irrotatable: Quantized Vortices in a Super-Gas!
The ultra-cold atomic gas of a Bose-Einstein condensate is reluctant to rotate -- it would prefer to remain at rest even when it is immersed in a rotating environment. Sometimes, however, nature simply insists, and the result is the spawning of quantum vortices, tiny, tornado-like objects that wend and wind their way through the sample. Stir a condensate hard enough, and you get dozens or hundreds of these little whirlstorms, and they start to interact with one another, forming intricate patterns.
Throughout Dr. Cornell's visit there will be numerous opportunities for students to visit with him individually and in small groups. For details, consult Professor Brandenberger.
Th 21 Oct 4:15~PM, Y-115: Physics Colloquium
Conductive Transparent Coatings: Smart Windows for Consumer Electronics
Thin film materials that are both electrically conducting and transparent serve as integral components of photonic devices such as solar cells for energy generation, fast switches for optical fiber communication, electrodes for flat panel displays, and large area panels for lighting applications. The difficulty in achieving this duality in a material is formidable since high conductivity, as in a metal like copper, is usually accompanied by low optical transparency. Over the past hundred years, two contrasting approaches have been used to achieve the desired film response: impart transparency to a metal without compromising conductivity or induce conductivity in a transparent material. Success in either approach requires the modified material to possess an abundance of mobile charge carriers. Both chemical and structural defects, intentionally introduced into these materials, generate charge carriers in these media, and it is these charge carriers that promote conductivity. Creating, modifying, and characterizing such films will be discussed, as will their uses.
Non-neutral plasma physics programs at the University of California--San Diego and Lawrence University
Professor Stoneking will describe his summer research work with plasma physicists at the University of California--San Diego. Physicists at UCSD pioneered non-neutral plasma physics and continue to produce the bulk of the results in the field. The talk will focus on electron plasma experiments carried out at UCSD and plans for a new toroidal electron plasma experiment at Lawrence University.
Th 18 Nov 4:15 PM Y-115: Physics Colloquium
Spin Coherence in Silicon/Silicon-Germanium Nanostructures
With a long spin coherence time, an electron trapped in a quantum dot in silicon/silicon-germanium is a prime candidate for a quantum bit (qubit) in a solid state implementation of a quantum computer. Dr. Truitt will discuss the approach chosen at the University of Wisconsin - Madison for building such a quantum computer, and discuss how his work measuring spin coherence fits into that plan, giving particular attention to the fabrication and characterization of devices that operate with single electron precision. He will show data on spin coherence of electrons in a two-dimensional electron gas and discuss attempts at Madison to understand the processes by which the electrons decohere. Finally, he will show how the Madison researchers plan to merge the two approaches and make spin measurements of individual quantum dots.
Analyzing Waveforms from Long-period Seismic Events
The degassing behavior of a volcanic system is an integral part of the seismicity it generates. Volcanic monitoring has relied heavily on the use of seismic networks and regular measurements of sulfur dioxide degassing to evaluate the state of the magma body and the potential for future eruptions. These methods have helped improve understanding of magma dynamics and eruption forecasting, but have been limited by the fact that gas measurements cannot be taken at similar temporal resolution as continuous seismicity. Thus, these methods, have remained somewhat independent of each other relaying on observing distinct changes or trends in activity as indicators of future events. However both decreasing and increasing trends in SO_2 emissions may signal impending eruption, and a closer link between seismic and degassing information would give scientists and new tool with which to mitigate volcanic hazards. In January 2002, the Montserrat Volcano Observatory installed a new gas monitoring system at Soufriere Hills Volcano composed of two Differential Optical Absorption Spectrometers (DOAS); these new sensors allow continuous retrieval of sulfur dioxide spectra from the emitted plume, and gas flux values every 1-6 minutes over the course of a working day. These data enable, for the first time, a close merging of gas and seismic data-sets.
During the summer of 2004, Paul Schonfeld conducted research at Michigan Technological University, assisting in the analysis of a group of seismic events at Soufriere Hills Volcano that occurred in July, 2002. A description of the project and results will be presented.
Einstein's 1905 Paper on Brownian Motion
The World Year of Physics 2005 marks the centennial of Albert Einstein's remarkable year (1905) --- the year in which he published five important papers. This talk will focus on his theoretical explanation for Brownian motion and on its enduring significance. Brownian motion refers to the zigzag motion of particles suspended in a fluid, as observed under a microscope. Among the several important results of this paper are (1) the derivation of a relation that was subsequently used to determine Avogadro's number to greater accuracy than had been achieved to date, thus helping to conclusively establish the reality of atoms and molecules, and (2) a convincing theoretical demonstration that diffusion results from the accumulation of successive, independent, randomly directed steps.
Bringing a Star to Earth: Confining and Understanding a High-Temperature Plasma
"Bringing a star to earth" is hyperbole, but the physics involved in confining and understanding a high-temperature plasma is exciting and at the forefront of science. The University of Wisconsin--Madison has been involved in plasma physics and fusion research for over 50 years, and continues to play a leading role in the field. One of the major U. S. plasma physics research facilities, the Madison Symmetric Torus (MST) Reversed-Field Pinch, is located on campus in the Department of Physics. This toroidal device magnetically confines a high-temperature plasma that is studied using a wide variety of diagnostic techniques. Many of these are optical or spectroscopic; two important diagnostic systems on MST will be described in more detail. The first, called Thomson Scattering, relies on the scattering of laser photons by the plasma electrons to determine the plasma temperature and density. The second, called Motional Stark Effect, uses a measurement of the Stark spectrum of hydrogen atoms to determine the magnetic (not electric) field in the plasma. These measurements, along with others, play a key role in modeling the equilibrium of the plasma and understanding the confinement of the plasma. This understanding has application both to the develoopment of a fusion energy source and to fundamental plasma astrophysics.
Powering LEDs for an experiment to trap single barium ions
During the summer of 2004, Lauren Kost participated in an REU Program at the University of Washington and worked on an experiment involving single, trapped barium ions that were used for Zeeman resonance measurements, parity non-conservation experiments, and atomic clocks. In this talk, she will address several aspects of the barium ion experiment as well as her contributions this past summer. Her main project was to build a circuit that would supply two to three amps of current to each of two high-power LED's.
Structures of lead-gallate glasses and quantitative analysis techniques for mass spectrometry
Duncan Ryan spent the summer of 2004 at Coe College studying the structure of the lead-gallate glass system. Analysis of mass spectra over varying compositions showed longer range networks forming in larger lead concentrations. The glass forms networks similar to the crystal form of the system. By using lead (IV) in place of lead (II), the glass forming range can be extended. In this talk, Duncan will report on the crystallization temperature, density, and optical properties measured for the extended range. While examining the spectra of the system, he developed quantitative techniques for analyzing the spectra and will report on their application to the lead-gallate system.
First Principles Band Structure Calculations
The calculation of the electronic structure has become one of the most powerful tools in the field of materials research because of its ability to predict the properties of new materials before they are created and characterized in the laboratory. Last summer Steve studied the plane wave method, a simple first principles method for calculating and understanding the properties of materials. He wrote a FORTRAN computer program that used the plane wave method to find the band structure, Fermi energy, and charge density of a periodic one- dimensional system. In addition, he has made several improvements to his original code. First, he extended his code to two dimensions and verified numerically that the wave functions he calculated were normalized and orthogonal. Lastly, Steve studied the Pseudopotential concept and implemented the Orthogonalized Plane Wave method, which address several shortcomings of the plane wave method. In this colloquium Steve will discuss the methods he used, as well as his results and hopes to give you a taste of why the calculation of the electronic structure has become such a powerful tool in materials research. This work was conducted as part of the Northwestern University MRSEC Summer REU-MRI Program and at Lawrence University as a senior Capstone project.
We 23 Feb 4:15 PM NSB 102: Science Colloquium
Christina Dunn, University College London and Zeeko, Ltd.
Extreme Astronomy: The Euro50 Telescope
The next generation of astronomical telescopes, called Extremely Large Telescopes (ELTs), is currently being developed. The Euro50 telescope, planned by a consortium of universities in Finland, Ireland, Spain, Sweden, and United Kingdom, is an example of one of these new generation telescopes with a primary mirror diameter of 50 meters, five times larger than the world's current largest telescope. Euro50's light gathering power will be greater than all existing telescopes combined. This talk will introduce some of the new technology being developed for these telescopes and the science planned for them when they are completed.
Th 10 Mar 11:10 AM Y-115: Physics Colloquium
Quarks, Gluons, and Asymptotic Freedom
Samridha Kunwar, LU '05
Saturated Absorption Spectroscopy and Hyperfine Structure in
83-Kr
April Evans, LU '05
As part of an ongoing Capstone Project, this talk will discuss the technique of saturated absorption spectroscopy and its use in examining hyperfine structure (and some other effects) in natural Krypton.
Th 7 Apr 11:10 AM Y-115: Physics Colloquium
Self-Organization in Magnetized Plasmas
It is a common process in the universe for plasma and magnetic fields to evolve together in a turbulent way but then rapidly relax to simple, self-organized structures. Solar flares erupt from the photosphere tangled and chaotic, but via a process called magnetic reconnection, they relax and straighten. This process releases energy in the form of superheated plasma and rapidly flowing jets. On a much larger scale (millions of light years), galactic disks collapse, rapidly shedding angular momentum and in the process generate extended, magnetized jets along their axes. On human scales, laboratory experiments are underway seeking self-organized magnetic structures that would be suitable ``bottles'' for a fusion reactor.
We present recent experimental results from the merger of two rings of hot, magnetized plasma in the Swarthmore Spheromak Experiment (SSX). During the merging process, the plasma self-organizes to generate a single, large scale (r=0.2 m, L=0.6 m), three-dimensional magnetic structure called a field-reversed configuration (FRC). The rate at which the merging proceeds is governed locally by magnetic reconnection in which magnetic fields associated with each ring become shared. The magnetic reconnection rate is fast and fully three-dimensional. Magnetic reconnection converts magnetic energy to heat (up to T_e=10^6 K), energetic particles (E_i > 100 eV), and flow (up to 100 km/s).
Further information can be found at a Swarthmore website.
Th 7 Apr 4:30 PM NSB-102: Science Colloquium
Astrophysics in the Laboratory
Modern laboratory techniques have recently enabled scientists to reproduce astrophysically relevant conditions in the laboratory. Intense laser pulses can reproduce conditions relevant in supernovae and astrophysical jets. High voltage, high current pulses of electricity can heat ionized gas (called plasma) to conditions found on the surface and corona of the sun. Typically, these conditions can only be reproduced in the laboratory for a short time (nanoseconds to microseconds) while conditions in astrophysical contexts can persist for millions of years.
This talk will consider several questions posed by solar physics and astrophysics and describe how these questions are being addressed in the laboratory. The questions include: How do stars burn so hot for so long? How do the sun and planets generate magnetic fields? Why is the sun's atmosphere (corona) 1000 times hotter than its surface (photosphere)? How do astrophysical objects generate energetic particles (cosmic rays)? How do astrophysical disks also generate extended magnetized jets sometimes a million light years long? These questions are related and are being addressed at a facility at Swarthmore College called the Swarthmore Spheromak Experiment (or SSX).
Joan Marler, University of California, San Diego. Ms.~Marler is a candidate for a position as a Lawrence Fellow in the Department of Physics.
When Anti-Matter Attacks
``When anti-matter attacks ... '' is the first line in a recent popular science article [E. S. Reich, New Scientist, 24 April 2004] highlighting research performed at UCSD. Seriously, there is no need for alarm but recent progress in the ability to accumulate, cool, and manipulate anti-matter is leading to an increased presence of anti-matter particles in fundamental research and in applications. I will discuss our group's stato-of-the-art scheme for positron (i.e., 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.
Confining Electron Plasmas in a Toroidal Magnetic Field or Plasma and Donuts: It's not just about blood donation anymore
Matthew Stoneking, Department of Physics, Lawrence University
Charged particles tend to flow along magnetic field lines like beads on a wire. This fact helps plasma physicists understand why the aurora appears near the earth's poles (hence "northern" and "southern" lights), and why the prominences on the surface of the sun have an arched shape. This fact is also exploited to confine hot plasmas (charged particles) in experiments that might lead to a new type of power source (fusion). Professor Stoneking will discuss some basic plasma physics experiments in which electrons are trapped in a toroidal (or doughnut-shaped) magnetic field, experiments that make connections to fusion experiments and space plasma physics.
Dr. Carroll will be arriving in the early afternoon on Monday, 2 May, and will be here until about 5:00 PM on Tuesday, 3 May. During that time students will have ample opportunity to interact with him individually and in small groups. Appointments can be made with Mr. Cook. Dr. Carroll will deliver two talks during his visit:
Mo 2 May 4:30 PM New Science 102: Science Colloquium
Our Preposterous Universe
The twentieth century witnessed breathtaking discoveries about the nature of the cosmos. We learned that the universe is over ten billion years old, that it is expanding, and that ordinary objects (stars, planets, human beings) comprise less than five percent of what the universe is made of. The challenge for the twenty-first century will be to develop a true understanding of what these discoveries mean. What is the dark matter and dark energy that makes up most of the universe? How did the universe begin? How will it end?
Tu 3 May 11:10 AM Y-115: Physics Colloquium
Why is the Universe Accelerating?
Our universe is accelerating, a phenomenon that cannot be accounted for by ordinary matter and conventional gravity. The simplest explanation is to invoke a vacuum energy of 120 orders of magnitude less than the expected amount. Alternatively, there could be a smoothly-distributed, slowly-varying dynamical component, or a breakdown of general relativity on cosmological scales. All of the possibilities are very exciting, and future observations have promise for distinguishing between them. I will give an overview of the theoretical proposals for explaining the acceleration of the universe and the observational constraints which any model must satisfy.
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.
Annual Reception for physics graduates and their graduation guests.