Department of Physics
SCHEDULED EVENTS (2007-08)
OTHER IMPORTANT DATES
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.
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.
DNA Trapping in a Silicon Dioxide Nanopore
William Dowd, LU '08
The feasibility of trapping DNA in a silicon dioxide nanopore using an electrostatic field has been investigated using a molecular dynamics approach. Proper construction of the nanopore system including an annealing cycle, energy minimization, and NPT equilibration are discussed. Molecular dynamics simulations on the constructed system demonstrate that a potential well resulting from the application of a positive bias to the silicon membrane forces DNA into contact with the pore surface, thereby retarding DNA translocation through the pore. Further experimentation with such systems could lead to an effective method for fast and cheap sequencing of DNA. This talk will report on work done in an REU at the University of Illinois during the summer of 2007.
A Seven-Year Photometric Study of Three Active Galactic Nuclei
Sarah Marheine, LU '09, and Kenneth Rumstay (Valdosta State)
In order to further our understanding of the structure of the broad emission-line region of AGNs, we have analyzed Seyfert galaxies 3C-120, Mrk 79, and Mrk 704 using relative and absolute photometric methods. This will hopefully lead to an ability to use reverberation mapping to estimate the geometry and mass of the central regions of these objects. We provide an overview of the current model of an AGN and a brief description of the technique of reverberatiion mapping. This talk will report on work done in an REU at the Valdosta State University in southern Georgia during the summer of 2007.
Tracking Insect Flight
Sarah Curry, LU '08
Interest in insect behavior and the insect's sense of sight has prompted research of an apparatus capable of tracking an insect in 3D. This apparatus has been developed and is presented here. The main components of this apparatus include a 5mW laser, a reflective material called Reflexite, a 4-quadrant diode, 3 electrical circuits, and a power supply. The electrical circuits direct the laser to capture the fly within the beam and follow its movement. This talk will report on work done in an REU at Indiana University during the summer of 2007.
Investigation into the Free Boundary of Liquid Crystals
Jeffrey Solberg, LU '09
Nanoscience concerns itself with the changes in the properties of materials at small scales. Often times this is accomplished via the creation of particles at nanoscale in all three dimensions. Liquid crystals offer us an opportunity to observe these changes when only one dimension is reduced by producing a liquid crystal film. The phase of 7O.7, the liquid crystal investigated, varies both with temperature and thickness of the film and includes the crystalline phases, smectic phases, and nematic phases,. We use an atomic force microscope in non-contact mode to preserve the soft surface, to investigate such materials when they are in the crystalline-B phase between 58 and 65 centigrade. The underlying physics of atomic force microscopy will be discussed. If the bulk phase and surface phases were equivalent for crystalline-B, we would expect a surface modulation which would appear in a Fourier transform. Preliminatry scans of crystalline-B indicate that this modulation is not present. Instead we see features, such as the flatness of the surface, on short length scales as well as steps, which suggest that the surface phase is smectic-F. This talk will report on work done in an REU under Professor Collett's supervision at Lawrence University during the summer of 2007.
An In Situ Characterization of the LIGO Optics
Russell Geisthardt, LU '08
Power loss due to absorption and scattering by the LIGO optics contributes to decreased laser power and increased shot noise in the LIGO interferometer. Improved characterization of this power loss allows for further improvements to the optics. The absorption by the mode cleaner optics was measured and modeled. The measurement was done by measuring the frequency shifts of the drumhead eigenmodes as the optic was heated. The modeling connected the frequency measurements to the power absorption. The absorption was found to be 18, 42, and 61 ppm for the mode cleaner optics. A study of the scattering from the core optics was also performed. The amount of scattered light was measured at different angles using a photodetector outside of the vacuum viewports. The results were used to determine how much of the total amount of light scattered was due to point defects and how much was due to microroughness. This talk will report on work done in an REU at Louisiana State University during the summer of 2007.
Orbit Modeling in Proto-Planetary Disk Simulations
David Meichle, LU '09
The formation of planetary systems, and specifically the mechanisms which produce large Jovian planets, is a subject of debate. One model suggests that regions in proto-planetary disks collapse due to gravitational instabilities and form gas giants directly. In our simulations, fragmentation regularly occurs and material coalesces into small, dense regions under appropriate conditions. It is possible that Jovian planets are then produced from these clumps. In simulation, however, these clumps tend to disappear shortly after forming. The destruction of dense structure may be due to real physical processes or due to a numerical artifact from inadequate grid resolution.
Recently, software modules were added to an existing second order three-dimensional hydrodynamics simulation. These modules extract and replace the clumps with point masses. Additional modules follow the orbital evolution of the point masses in the disk. This procedure may remove effects of inadequate grid resolution. Preliminary results show that the clumps do not, in fact, form in stable orbits. In less than one orbital period they either fall into the central star or leave the computational grid. Further testing will investigate a variety of initial disk configurations. This talk will report on work done in an REU under Professor Pickett's supervision at Lawrence University during the summer of 2007.
Informal Discussion of the National Virtual Astronomical Observatory
Dr. Robert Hanisch, LU '76, and principal architect of the NVAO
Effects of the Columbia River Plume on the Dynamics of Upwelling
off Oregon
Daniel Fulton, LU '09
The Regional Ocean Modeling System (ROMS) has been utilized to study the effects of the plume from the Columbia River (CR) on the dynamics of upwelling south of the river mouth over the Oregon shelf, where the river water is advected with a coastal current. The study period is summer 2001, for which observations from the COAST and GLOBEC programs are available to verify the model accuracy, including shelf mooring observations and hydrographic sections. Effects of the CR are analyzed by comparing simulations with and without CR. The depth of the surface boundary layer (SBL) and the level of turbulent kinetic energy in the SBL are influenced by both the enhanced vertical stratification and increased vertical shear in the horizontal velocity, which is related to the plume-induced horizontal gradient of density. Within the plume, the Ekman transport is distributed in a thinner SBL, resulting in larger surface cross-shore velocities. Analyses in an idealized alongshore-uniform configuration show that if the plume is attached to the coast, upwelling is concentrated closer to the coast than in the case without the fresh water layer. This work was done in an REU in the summer of 2007 with A. L. Kurapov, S. Springer, J. S. Allen, J. A. Barth, and P. M. Kosro of Oregon State University and with B. Hickey of the University of Washington.
Magneto-Optical Trapping and Cooling of Rubidium
Gennady Malyshev, LU '09
A magneto-optical trap (MOT) for the purpose of trapping and cooling rubidium atoms has been constructed. The science of magneto-optical trapping as well as the details of the trap's construction will be discussed. This talk will report on work done in an REU under Professor Brandenberger's supervision at Lawrence University during the summer of 2007.
Effects of Vortex Ring Induced Drag on Oscillating Pendulum Decay
Andrew Phillippi, LU '09
Tests have been done to observe the effects of vortex rings on the drag of a pendulum oscillating in water. The experiments took place over the summer of 2007 during which, the equations used to model the amplitude decay of a pendulum swing were shown to be fundamentally different than what they had previously been thought to be. The effects of vortex ring shedding were observed using a pendulum oscillating in a tank of water using the Baker technique to observe the amplitudes of swing at which vortex rings are shed and comparing them against the inconsistencies found in the measured decay rate of the pendulum swing. Whether or not vortex rings are shed is governed by the Keulegan- Carpenter (KC) number which is a dimensionless ratio of the amplitude of the swing to the diameter of the spherical pendulum bob. At low KC numbers (and thus high amplitudes) vortex rings are shed and the decay is much greater than a standard exponential decay rate that is expected from a decay due to drag. At high KC numbers, the decay matches the expected decay rate. The amplitude decay becomes exponential at the same time that the system stops shedding vortex rings. It was found that each vortex ring that the system sheds causes it to lose a discreet amount of kinetic energy on top of that lost to the drag of the viscous fluid. This work was done in the summer of 2007 with R. Hershberger, D. Bolster and R. Donnely of the University of Oregon.
Introducing a Ratcheted Surface to a Turbulent Fluid
Max Halverson, LU '08
The Brownian Ratchet is a tiny motor, driven purely by thermodynamic effects. Richard Feynman used the Brownian Ratchet as a thought experiment in supporting the Laws of Thermodynamics. Today, these Brownian motors have shown numerous applications in quantum studies, microbiology, and fluid mechanics. In continuing these studies, experiments have been done to determine if Brownian motion type effects are present in turbulent fluids with the introduction of a ratcheted surface. This work was done in the summer of 2007 at the University of Oregon.
Numerical Modeling of Normal Modes of Oscillation in Two-Dimensional
Membranes
Russell Geisthardt, LU '08
The standing wave problem for a square membrane and an L-shaped membrane has been numerically modeled using the finite difference method. The numerical solutions for the square membrane are compared with the analytical solution, and the numerical solutions for the L-shaped membrane are compared with the solutions for the square membrane. This talk is a report on the end-of-term project in a tutorial in computational physics supervised by Professor Cook.
Protoplanetary Disk Simulations in a Binary Star System
William Dowd, LU '08
The effects of a binary star system on the formation of protoplanets via gravitational instabilities in a protoplanetary disk is investigated. The presence of a binary star is shown to have a destabilizing effect on the disk, and may make proto-planet formation easier. The rotation of the disk and star about a common center of mass also induces centrifugal and coriolis force terms within the disk which profoundly effect the development and stability of proto-planets. This talk is a report on a capstone project conducted in the fall of 2007 under the supervision of Professor Pickett.
Fear and Loathing in the Protoplanetary Neighborhood
Robert Maas, LU '08
We use a 3-D hydrodynamics code to evolve gravitationally unstable disks under the condition of local isothermality, and characterize the appearance and fragmentation of spiral arms in a disk as a function of the Toomre Stability Parameter Q, which measures the stabilizing effects of pressure, orbital speed and eccentricity versus the destabilizing effect of self-gravity. We find that for higher values of Q, the growth of unstable spiral modes is indeed slowed, and the onset of fragmentation is delayed or even prevented. Additionally, the number of spiral arms decreases. These results indicate that gas giant protoplanets are more likely to form, and that more may form, in cooler disks. The long term survival of these protoplanets remains uncertain. This talk is a report on a capstone project conducted in the fall of 2007 under the supervision of Professor Pickett.
Physics Power: A Sampling of Physics Problems Applicable to Energy
Technology
Sarah Curry, LU '08
The growing concern surrounding fossil fuel emissions and the general interest in keeping energy costs low has led to interest in further development of energy systems. With a focus on alternatives to fossil fuels, this work presents a small sample of the physics problems underlying energy technology systems. The featured problems include a heat exchange problem applicable to fossil fuel and nuclear power plants, a derivation of the potential energy field around three transmission lines, and an analysis of the forces on a wind turbine blade. Systems that utilize nuclear power, hydropower, and hydrogen power are also investigated. This talk reports on a project carried out in the fall of 2007 under the supervision of Professor Stoneking.
Purely Toroidal Confinement of a Non-neutral Plasma
Jason Smoniewski, LU '09
According to theory, there is an equilibrium state for a non-neutral plasma trapped in a purely toroidal magnetic field. However, this equilibrium is dependant on image charges induced on a conducting wall near the plasma. The image charges create an electric field to counter the normal plasma drift due to the magnetic field gradient. Professor Stoneking's Lawrence Non-neutral Torus ( LNT ) achieved this equilibrium state for unprecedented durations (18 ms), and the LNT II has improved on the design enabling more accurate data and longer trapping times (3 s). This summer has been dedicated to redesigning and rebuilding the electron source, understanding the theory of the torus, and building electronic circuits to improve the quality of the data and the lifetime of the plasma. This talk reports on work carried out in during the summer of 2007 under the supervision of Professor Stoneking.
Optimization of CESR-c Optics for High Time-Integrated Luminosity
Mackenzie Van Camp
The Cornell Electron Storage Ring (CESR) operates at world-record production rates for bound states of charm quarks. Its success depends on maximizing particle collisions by managing the interactions between its oppositely charged, counter-rotating e-/e+ beams. Two methods for regulating these interactions are adjusting the beam current and altering the separation between the beams, but in some cases these can actually reduce the total number of particle collisions. We describe a modeling algorithm which optimizes operating currents and orbit separations. The algorithm successfully finds values for the beam current and orbit separation which are likely to increase the time-integrated collision rate, making it a useful new tool for optimizing CESR's optics. This work was done in the summer of 2007 at Cornell University.
The Industrial Physicist
Join Dave Meichle's mother Dr. Linda S. Barton, Professor of Physics at the Rochester Institute of Technology and former Experimental Physicist at Eastman Kodak company, and Dave Meichle's grandfather, Dr. Mark. Q. Barton, Accelerator Physicist Emeritus at Brookhaven Laboratories and Experimental Physicist Emeritus at IBM, for a free-wheeling discussion of such topics as: (a) What to do with a physics degree; (b) What an industrial physuicist actually does day to day, (c) Stories from the experimentalists; (d) Career paths in experimental physics; (e) Physics outside the University; ...
Using a green-pumped MgO:PPLN optical
parametric oscillator to measure coherent anti-Stokes Raman
scattering in organic compounds
Erik T. Garbacik, LU '08
In the fields of medicine and biophysics, knowledge of the mechanisms of complex biological reactions can be very difficult to obtain, especially in situ. Many current techniques, such as tagging with radioactive compounds or fluorescent dyes, rely on invasive procedures that can affect the native processes adversely and generate undesirable results. To develop a highly accurate, high-resolution, non-invasive method for investigating intra-cell behavior is a primary goal for researchers in these fields. A promising candidate to fulfill this role is Coherent Anti-Stokes Raman Scattering (CARS), a four-photon process that, through conservation of energy and momentum, produces collimated light that can be analyzed to determine vibrational resonances down to the single-molecule level. Precise tuning of the input beams allows specific resonances to be excited, and continuous scanning of the pump lasers yields entire infrared spectra, which provide possibilities for simultaneous imaging and spectroscopy. CARS boasts a number of benefits over traditional IR and Raman spectroscopy in that it is immune to fluorescence, is highly collimated, and can be easily filtered via spatial and/or spectral methods. The primary source of the tunable input beams to obtain CARS is the optical parametric oscillator (OPO). In this experiment, the OPO is based on a periodically-poled magnesium oxide-doped lithium niobate (MgO:PPLN) crystal, allowing access to molecular vibrational resonances in the 215-4200 cm-1 range. We have recently recorded the spectrum of PMMA (polymethylmethacrylate) in the ``fingerprint'' region near 1000 cm-1 and are working to measure at even lower wavenumbers. This talk will report on work performed during the summer and fall of 2007 in the Optical Sciences group at the Universiteit Twente in Enschede, Netherlands.
Understanding Dense Star Clusters Through Simulation
Shawn Slavin, Purdue University--Calumet
Dense star clusters, such as massive young clusters in nearby galaxies and globular clusters around galaxies such as our own, exhibit evolution which is driven not only by their overall self-gravity but by complex interactions involving two, three or more stars in their dense core environments. A proper understanding of the how the evolution is affected by hard scatterings, binary formation, and exchange interactions must be modeled on a star-by-star basis through methods generally referred to as "N-body" methods. In this talk, I will describe the overall problem, discuss what can be gained from a better understanding of these evolutiionary patterns, and describe methods in use today. The nature of special-purpose computers, called "GRAPEs," designed specifically to accelerate these simulations, will be presented, as well as results of recent simulations of globular cluster dynamics.
Electron Spins: Building Blocks for the Quantum Computer
Shannon O'Leary, University of Oregon
The superior processing speed and capacity of a fully functional quantum computer will potentially revolutionize computational problem-solving and our understanding of quantum mechanical systems. The challenge of physically realizing the quantum computer motivates our research on controlling electron spins in semiconductors. The idea is to initialize the spins, control them, and then detect them using light. In this way information can be stored in the material, be processed, and then be read out. In this talk I will introduce semiconductor optics, describe our experimental approach to controlling electron spins, and present some recent results. Ms. O'Leary is a candidate for a position as Physics Fellow at Lawrence.
The Solar System in 3-D, and the Latest News from Saturn
Nick Schneider, Department of Astrophysical and Planetary Sciences,
University of Colorado
The robotic explorers sent by spacefaring nations have photographed every major planet and most of their moons, but rarely have these images been displayed as human explorers would experience them: in three dimensions. A special collection of 3-D images not only reveals the inner workings of the planets, but also helps us humans experience the sensation of visiting these other worlds. (3D glasses provided.) In the second part of the talk (without the glasses), I'll fiocus on some of the most recent and most amazing discoveries of the Cassini spacecraft now orbiting Saturn, exploring the planet, its rings, and moons. Dr. Schneider's visit is supported by the Harlow Shapley Visiting Lectureship Program of the American Astronomical Society.
Jupiter's Magnetosphere: A Volcano-Powered Nebula
Nick Schneider, Department of Astrophysical and Planetary Sciences,
University of Colorado
Jupiter's moon Io undergoes more volcanic activity than any other world in our solar system, despite its small size. Jupiter's charged particle belts glow more brightly than any other planet's, and fuel the most powerful auroras ever seen. In this talk I'll show how these remarkably different phenomena are intimately linked through connections that span the field of modern planetary science. I'll also describe how the surprising lessons of the Jupiter-Io system are leading to new insights in Saturn's moons, the evolution of Mars' atmosphere, and the question of planetary habitability.
Ducted Fans and Flying Machines Near Solid Boundaries
Andrew Kane, LU, '08
The thrust of a ducted fan is measured in proximity to an infinite plane. The distance to the plane and the relative angle of the plane are varied, and the results of the experiment are used to motivate an indoor, hovering remote control aircraft design. The results also challenge a popular causal explanation of the ground effect, and introduce a "ceiling effect" not found in formal literature.
Magnetic Fields in Astrophysics: Their Origin and Evolution
Ellen Zweibel, Departments of Physics and Astronomy, University of
Wisconsin - Madison and The Center for Magnetic Self Organization
,Astrophysical bodies--planets, stars, and the tenuous gas within and outside of galaxies---carry magnetic fields. In many cases, the fields are strong enough to influence the dynamics of these bodies, and they can release their energy rapidly and in spectacular ways. Yet, despite much progress in cosmology, we do not know how these fields originated or how they evolve. I will present some observations and current ideas.
Neutrinos from the Sky and Through the Earth
Kate Scholberg, Department of Physics, Duke University
The progress in neutrino physics over the past ten years has been tremendous: we have learned that neutrinos have mass and change flavor. I will pick out one of the threads of the story---the measurement of flavor oscillation in neutrinos produced by cosmic ray showers in the atmosphere, and its confirmation in long distance beam experiments. I will present the history, the current state of knowledge, and how the next generation of high intensity beam experiments will address some of the remaining puzzles.
Neutrinos from the Sky and Through the Earth
Kate Scholberg, Department of Physics, Duke University
Neutrinos are among the elementary constituents of matter, and understanding of their properties is crucial for understanding the overall features and history of the universe, But neutrinos are also slippery characters: they have only extremely feeble interactions with matter, and hence heroic efforts are required to detect them. Over the past decade, massive underground experiments have brought tremendous new knowledge about neutrinos. This talk will discuss the history, the current state of knowledge, and the remaining puzzles.
Photo Shoot: 4:30 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.
How I Found Strong Coupling in
Denmark: CQED Experiments with
Coulomb Crystals
Joan Marler, University of Aarhus
Cavity quantum electrodynamics (CQED) provides for the study of light-matter interaction at the level of single quanta. Within recent years, experimental progress has made it possible to trap even single atoms inside small optical cavities making the coherent process of photon-atom coupling faster than any dissipative processes, such as spontaneous emission and cavity decay. In this so-called strong coupling regime, CQED holds great promise as a tool for quantum information science where an efficient light-matter interface is in high demand for many applications.
Clouds of cold ions represent an interesting alternative system to a single atom/ion for studying CQED effects. When a trapped cloud of ions is cooled below a certain critical temperature, the ions form a spatially ordered state, referred to as an ion Coulomb crystal. We have succeeded in trapping such ion Coulomb crystals inside a high finesse optical cavity. The number of 40Ca+ ions in the cavity mode is sufficient to access the strong collective coupling regime, where the Rabi frequency corresponding to the collective coupling of the ions to a single cavity photon exceeds both the spontaneous and the cavity decay rates. We have recently seen the first signals of collective strong coupling in this system, most dramatically manifested via the vacuum Rabi splitting.
Investigation of Single Molecule Tracking
David Meichle, LU '09
Many interesting cellular process occur on nanometer scales but are unobservable with traditional optical microscopy, which is diffraction-limited to micrometer scales. We are specifically interested in nanometer scale dynamics of the kinesin molecule, a motor protein responsible for transporting a variety of cellular cargo. This can be accomplished by single molecule fluorescence microscopy, where a single fluorophore is attached to a sample. The fluorophore is imaged with a CCD camera and appears as a diffraction limited spot of radius ~250 nm. Observations in the unresolvable nanometer scale become a matter of localizing the fluorophore, or precisely finding the center of the diffraction spot.
A theoretical limit for the best possible localization recently appeared, and depends quantitatively on the image quality. We wish to systematically test this limit with existing tracking software and see if improvements can be made. Simulated images of single fluorophores are generated with defined image quality and exact knowledge of the fluorophores' location. These images are tracked and the found positions compared to the known positions.
Currently, we see that the localization software is roughly five times less precise than the predicted limit and does not behave as expected. Time permitting, we hope to improve the tracking software with a more robust, non-linear least squares fit instead of the simple averaging algorithm used now. These results give a quantitative comparison of the tracking software's precision with the predicted limit. This comparison will be important in future studies of nanometer scale motions of the kinesin molecule. (This talk will report on work conducted during Term III under the supervision of Professor Douglas Martin.)
Experimental Total Internal Reflection Fluorescence Microscop
Robert Niederriter, LU '10
Fluorescence imaging techniques have long been used to observe cellular functions on the micrometer scale, but these often face the problems of blurring and noise associated with out-of-focus fluorescent molecules. Total Internal Reflection Fluorescence Microscopy (TIRFM) can be used to make time-resolved measurements of the position of single molecules with nanometer precision. Such small precision is useful for imaging molecular processes such as the motor protein kinesin “walking” along microtubules.
TIRFM only illuminates a thin layer of the sample (approximately 200 nanometers), greatly reducing the blurring effects from out of-focus fluorophores. With sufficiently small concentrations of fluorophores in the sample and the help of computer software, position measurements of single molecules can be made with nanometer precision. I constructed a TIRF microscope from scratch by directing a focused laser beam into a high numerical aperture objective. The custom design makes the microscope more flexible, allowing the imaging of multiple fluorophores at once with different colored laser beams. (This talk will report on work conducted during Term III under the supervision of Professor Douglas Martin.)
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.