Bulletin of the American Physical Society
2005 7th Annual Meeting of the Northwest Section
Friday–Saturday, May 13–14, 2005; Victoria, BC, Canada
Session C1: Posters |
Hide Abstracts |
Room: MacLaurin (outside 144) 5:00-6:30 pm |
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C1.00001: Measuring and Modeling Liquidus Temperature in High-level Nuclear Waste Glasses Jonathan Hanni, Eric Pressly, Kevin Minister, Jarrod Crum, John Vienna, Theodore Besmann, Karl Spear The U.S. Department of Energy (DOE) is currently constructing the world's largest vitrification facility at the Hanford Nuclear Reservation in Richland, Washington. The goal of this facility is to reduce current environmental threats caused by liquid nuclear wastes by melting them into stable oxide glasses. Glass compositions must be chosen which will optimize durability and waste loading. Crystallization is one of the main limiting conditions for both durability and waste loading. Liquidus temperature (T$_{L})$, defined as the temperature below which the melt will begin precipitating crystalline phases, can be used to determine optimum melting conditions and glass compositions. Currently, a modified associate species model (ASM) has been developed to predict T$_{L}$ and primary phase as a function of melt composition. In this work, model predictions are compared with measured data for 42 different melt compositions within the Al$_{2}$O$_{3}$-B$_{2}$O$_{3}$-CaO-Na$_{2}$O-SiO$_{2}$ chemical network. Data have also been measured for glass melts that include 7 additional oxides common to Hanford waste. These will be used as benchmarks for comparison as the ASM is expanded. [Preview Abstract] |
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C1.00002: Comparing quantum and classical correlations in a quantum eraser Ashifi Gogo, William D. Snyder, Mark Beck We have demonstrated the operation of a quantum eraser based on a polarization interferometer. Which-path information is erased not by modifying the interferometer apparatus, but instead by modifying the information obtained from measurements performed on a second beam, whose polarization is correlated with that of the interferometer beam. We compare the results obtained when the two beams are in an entangled state (quantum correlations) and in a mixed state (classical correlations). We find that classical correlations can mimic most, but not all, of the quantum mechanical behavior. [Preview Abstract] |
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C1.00003: Ferromagnetic resonance and stress anisotropy in ferromagnetic/anti- ferromagnetic bilayer Guo Hong Yun, Jian Hong Rong, Donald Sprung Magnetic multilayers often exhibit giant intrinsic stress due to the deposition process and the consequent increase of stress magnetic anisotropy energy. To understand the intrinsic stress of materials in order to improve their performance in applications, the effect of applied MPa uniaxial in-plane stresses on the ferromagnetic resonance (FMR) behaviour of magnetic bilayers, which consist of a ferromagnetic film coupled to an antiferromagnetic film, was investigated theoretically. The FMR modes which depend on the applied magnetic field angle, the exchange anisotropy, especially the stress anisotropy and its angle to the bilayer system, are obtained for different values of applied stress. Emphasis is placed upon understanding properties such as the positions, linewidths, and the angular dependence of the FMR frequencies and linewidths. A general theory of applied strain and stress is proposed. Comparison with previously reported theoretical results is made, and the need to measure certain physical parameters is highlighted. [Preview Abstract] |
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C1.00004: Can magnetic waves in aurorae transform into acoustic waves? Jada Maxwell, E.J. Zita Acoustic waves from the Sun's photosphere transform into magnetic waves in the chromosphere (Johnson et al., 2001; Bogdan et al., 2000, 2002, 2003). While there is no clear evidence of audible sound in aurorae (e.g. northern {\&} southern lights), infrasound (acoustic waves below 20 Hertz) emanating from aurorae has been detected. How are these auroral acoustic waves created? Alfv\'{e}n waves in the Earth's magnetosphere have been observed to arise from solar magnetic storms.~ Can these magnetic waves similarly transform into acoustic waves? On the Sun, this acoustic-to-magnetic wave transformation occurs where the atmospheric pressure and the magnetic pressure are comparable (beta $\sim $ 1), in the chromosphere.~ This wave transformation is crucial for transporting photospheric energy to the hot corona. We investigate evidence and mechanisms for magnetic-to-acoustic wave transformation in the Earth's ionosphere, where beta $\sim $ 1. [Preview Abstract] |
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C1.00005: Phase transitions in K2Cr2O7 and structural redeterminations of phase II Peter Wu, T.J.R. Weakley, E.R. Ylvisaker, R.J. Yager, J.E. Stephens, R.D. Wiegel, M. Mengis, M.R. Bauer, Panos Photinos, Sidney Abrahams The phase transition in K$_{2}$Cr$_{2}$O$_{7 }$has been studied and speculated upon inconclusively since 1908. We show that crystals of phase II with space group $P$, as grown from aqueous solution, undergo a first-order transition to phase I, space group $P$2$_{1}$/$n$, at $T_{PT}$ = 544(2) K on first heating. $T_{PT}$ on cooling is 502(2) K; on subsequent heatings, $T_{PT}$ = 531(2) K, 502(2) on cooling. The mass loss between \textit{$\sim $}531 and 544 K is identified as water that increases$ T_{PT}$ on first heating due to the pressure of superheated water in inclusion defects. The structure of phase I that we inferred has been investigated by high temperature powder diffractometry, that of phase II independently redetermined by single crystal diffractometry. The details of the large rotations of atomic groups as symmetry elements are gained or lost at the first order phase transition will be discussed. A first order transition between the recently discovered phase IIb and that of phase I is likely but not between phases II and IIb. An intermediate phase may exist between phases IIb and I. \textbf{Financial support by National Science Foundation (DMR-9708246, DMR-0137323)} [Preview Abstract] |
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C1.00006: A Rubidium Atom Magneto-Optic Trap Evan Carlson, Daniel Roberson, Shannon Mayer We present the theory and experimental apparatus for a magneto-optic trap for rubidium atoms. Laser cooling and magneto-optic trapping of atoms is a relatively simple but effective tool for producing high-density, low-temperature atomic samples. Operation of the MOT relies on radiation pressure from three orthogonal pair of counterpropagating laser beams to exert a force on the atom. By tuning the laser slightly below the atoms' resonance frequency, a moving atom will be Doppler shifted closer to resonance with one of the opposing laser beams and farther from resonance from the other. The resulting imbalance in absorption probability provides a velocity-dependent force to damp the atoms' velocity. Atoms are ``trapped'' with the addition of a spatially dependent confining force provided by a weak, inhomogeneous magnetic field. The apparatus for our experiment consists of an ultrahigh vacuum system, two tunable grating-feedback diode lasers, and the associated optics and electronics. A simple, current-adjustable rubidium oven provides for rapid control of the rubidium pressure in the vacuum system. CCD camera images show rubidium fluorescence in the trap region. [Preview Abstract] |
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C1.00007: Nanosecond spectroscopy of trapped ion samples in a linear Paul trap Louis Poirier, Robert I. Thompson This presentation will examine the use of visible nanosecond laser pulses to characterize trapped ion samples through the application of laser-induced fluorescence (LIF) spectroscopy techniques. A XeCl pumped dye laser system is used to produce tunable nanosecond laser pulses in the visible and ultraviolet region of the spectrum. The LIF spectra, detected at 105\r{ } to the incident laser path, can be used to non-destructively identify trapped ion species, and to determine some physical characteristics of the species, such as temperature. Experiments currently on-going in the laboratory include using LIF for ion-trap mass spectrometry (ITMS) calibration, and attempting to directly measure the rotational temperature of trapped CO$^{+}$ via ro-vibronic spectroscopy of the X -- A transition near 455 nm.\newline \newline This work is supported by NSERC. [Preview Abstract] |
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C1.00008: Auto Image Recognition of Chaotic Vortex Creation in Taylor-Couette Flow Nicholas Carroll, Richard Wiener, Thomas Olsen We partially automated the detection and tracking of phase-slips (i.e. vortex creation events) for fluid flow in the gap between a rotating inner hourglass and a fixed outer cylinder (a modified Taylor-Couette system). Using a gray scale digital camera, we recorded static images of the vortex pattern at set time intervals. The recorded images were saved as a single array of pixels corresponding to a 1D slice of the pattern. Vortex centers are lighter than their boundaries, making the array into a waveform with maximum values representing the centers of vortices. Using a correlation function between subsequent frames we could detect frames that had more vortices than previous ones. This allowed for the recognition of a phase slip. The resulting correlation values can be graphed versus time, and the time interval between sharp drops in correlation indicated the time between phase slips. The peak of our correlation waveform would drift in accordance with the drift of the vortices, making possible the determination of overall drift direction between phase slips. The time intervals and drift directions determined by our detection and tracking method compared well with previously observed chaotic pattern dynamics for this system. [Preview Abstract] |
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C1.00009: A method for getting the absorption spectrum from the interference fringes of a thin film P.K. Lim, W.K. Tam, K.K. Ng In measuring the absorption spectrum of a weak absorbing thin film, one always faces the problem of detecting a small signal buried in background noises, which is further complicated by the interference effect and the reflection lost at the surface. The way for extracting absorption spectrum from experimental data is usually quite involved. We have carefully studied the interference fringes of a thin film and have come up with a method to obtain the weak absorption spectrum from the amplitude of the interference fringe of a thin film. The method is less tedious and in certain extent eliminates the background noises and the intensity instability of the light source. The method has been successfully applied to obtain the absorption spectrum of an amorphous silicon thin film. [Preview Abstract] |
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C1.00010: Production of highly polarized $^{3}$He for magnetic resonance imaging Richard Jacob, Kevin Minard, Doug Wiseman, Brian Saam Spin-exchange optical pumping (SEOP) is the main method used to laser-polarize liter quantities of $^{3}$He gas for MRI applications. A major drawback is that 12-24 hours are normally required to achieve about 40{\%} polarization. We describe a high-throughput SEOP apparatus with rapid $^{3}$He polarization times (2-3 hours) and high polarizations ($>$50{\%}) by using a 60 W spectrally narrowed diode-array laser and hybrid optical spin-exchange (Rb-K). Individually, a narrowed diode laser has been shown to improve polarization levels by about 20{\%} [1], and hybrid SEOP increases spin-exchange efficiency by about 10 times [2]. Here, simultaneous use of both advances is described. We also examine the use of $^{3}$He dilution with a heavy buffer gas to slow $^{3}$He diffusion and thereby improve spatial resolution in $^{3}$He MRI experiments. [1] B. Chann, E. Babcock, L.W. Anderson, T.G. Walker, W.C. Chen, T.B. Smith, A.K. Thompson, T.R. Gentile, J. Appl. Phys. \textbf{94}, 6908 (2003). [2] E. Babcock, I. Nelson, S. Kadlecek, B. Driehuys, L.W. Anderson, F.W. Hersman, T.G. Walker, Phys. Rev. Lett. \textbf{91}, 123003 (2003). [Preview Abstract] |
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C1.00011: Phase Stabilization of a Modelocked Ti:sapphire Laser T.J. Hammond, Jie Jiang, David Jones The frequency stabilization of pulsed, mode-locked lasers has lead to an entirely new set of experimental capabilities (Jones et al, Science 2000; Diddams et al, Science 2001). When stabilized, the laser spectrum consists of a set of well-defined modes, collectively known as a frequency comb. In order to implement phase stabilization of a femtosecond mode-locked laser, an octave of bandwidth is required (Fortier et al, Opt Lett 2003). We have constructed a laser that directly generates this necessary octave. This poster will present the setup of an octave spanning Ti:sapphire femtosecond laser and the frequency locking scheme. By frequency doubling the low end of the spectrum and optically heterodyning it with frequencies at the high end, we are able to derive the offset frequency and stabilize the frequency comb in an absolute sense. Once stabilized in this manner, the comb can be used as a ruler for optical frequency measurements. We will discuss the future plans involving the use of our stabilized frequency comb as a spectroscopic tool for investigations into cold atom dynamics. [Preview Abstract] |
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C1.00012: Electron spin exchange coupling in semiconductor quantum dot pairs J.M. LaForge, G.M. Steeves Semiconductor quantum dots possess characteristics such as energy state spacing and a reduction of environmental interaction that make them appealing candidates for holding quantum information. Electron spin qubits within semiconductor quantum dots can interact with each other through tunneling exchange coupling. Similar experiments using coupled quantum wells and molecular bridged quantum dots have used Time Resolved Faraday Rotation (TRFR) optical techniques to probe and excite spin-states within the sample. TRFR is therefore a natural choice for further studies of electron spin states in semiconductor quantum dots. Dynamic control over the spatial separation of two adjacent quantum dots will allow us to study the spatial dependence of spin exchange coupling between dot pairs efficiently. Temporal control over the exchange coupling and its affect on the spin-state dynamics will also be explored. [Preview Abstract] |
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C1.00013: Parity Operator for One Dimensional Quantum Oscillator Patrick Bruskiewich A novel and simple derivation of the parity operator for a one dimensional quantum oscillator, using a unitary transformation and the annihiliation and creation operators, is presented. The derivation has pedagogical application to the teaching of quantum mechanics. [Preview Abstract] |
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C1.00014: The effect of size distributions of magnetic nanoparticles on the AC magnetic susceptibility as Biomolecule Sensor Joseph Nutting, Amit Sharma, Jiji Antony, Daniel Meyer, You Qiang Magnetic nanoparticles in a liquid have two relaxation times, N\'{e}el, $\tau _{N}$, and Brownian relaxation, $\tau _{B}$. For particles larger than 10-20nm, $\tau _{N}$ quickly becomes much larger than $\tau _{B}$ and can be ignored. $\tau _{B}$ is from rotation of the particle, and has a relaxation period from 10$^{-1}$ to 10$^{-5}$ seconds. This causes the imaginary part of the AC magnetic susceptibility, $\chi =\chi '$ + i$\chi ''$, to display a maximum at a frequency $f$ = 1/2$\pi \tau _{B}$. $\tau _{B}$ is related to the particle's size and can be used to create a sensor capable of detecting molecules. Because this is based on particle size, a size distribution will broaden the curve and reduce the sensitivity. Several groups have reported theoretical and experimental research results using this kind of sensor to detect biomolecules but have not paid attention on the size effects of sensitivities. Our group has synthesized monodispersive nanoparticles with size distribution less than 5{\%}, and calculated the effect of size distribution of magnetic nanoparticles on the AC susceptibility. E-Mail: ouqiang@uidaho.edu; Supported by NSF-EPSCoR, NIH-INBRE. [Preview Abstract] |
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C1.00015: Beyond the Arbitrariness of Ionic or Covalent Radii: Determination of Effective Atomic Radii in Solids from Electron Density Rafal Bachorz, Ivan Yakovkin, John Jaffe, Maciej Gutowski Effective atomic radii, net atomic charges, and projected densities of states are useful parameters for the evaluation of properties of solids. Within typical plane-wave expansion methods, atomic radii are required to carry on the population analysis. Unfortunately, there is no unique recipe how to determine effective radii. Tabulated sets of radii are commonly used, which do not reflect the specifics of chemical bonding in a particular solid. When using tabulated radii one frequently recognizes that a significant fraction of electron density is not assigned to any atom and the sum of projected densities of states (PDOS) poorly reproduces the total density of states (DOS). We propose a variational approach based on the charge density in the unit cell to determine effective atomic radii. The radii are constrained by a condition that the sum of volumes of spheres assigned to atoms should be equal to the volume of the unit cell. The radii are considered to be optimal when the total electron charge contained in a volume that is spanned by the atomic spheres has the maximal value. The optimal radii are system dependent and illustrate the effect of environment on charge distribution on each atom. [Preview Abstract] |
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C1.00016: Protein Structure and Folding Pathway Prediction Roy Campbell, Andrew Kruger We present \textit{ab initio} predictions of the three-dimensional structures of the folded proteins Dictyostelium V4-lmcA and V4-lmcB. Beginning with linear sequences of amino acid residues, we use a Monte Carlo fragment insertion method for protein tertiary structure prediction (ROSETTA) merged with the I-SITES library of sequence structure motifs and the HMMSTR model for local structure in proteins available on a public server. These 160-residue proteins differ by just two residues but have significantly different predicted structures. We use the HMMSTR-CM contact map method to predict folding pathways and steered molecular dynamics (NAMD, VMD) to simulate the mechanical unfolding of the predicted structures. [Preview Abstract] |
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C1.00017: A Program of Reaction-Diffusion Model Simulations of Modified Taylor-Vortex Flow in Systems of Varying Length Yu Hou, Thomas Olsen, Richard Wiener We seek to inform an experimental program of study of Modified Taylor-Vortex Flow with Hourglass Geometry\footnote{Richard J. Wiener \textit{et al}, Phys. Rev. E \textbf{55}, 5489 (1997).} in systems of varying lengths. These systems are modeled with Reaction-Diffusion equations.\footnote{H. Riecke and H.-G. Paap, Europhys. Lett. \textbf{14}, 1235 (1991).} For short systems, the formation of phase slips (corresponding to the formation of new pairs of Taylor-Vortices) occurs in a narrow range of positions near the waist of the hourglass. As the system length increases, the range of positions at which phase slips occur increases sharply, suggesting a transition from purely temporal to spatio-temporal chaos. Details of the simulations will be presented. [Preview Abstract] |
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C1.00018: Fractal Dimension of Experimental Time Series in Modified Taylor-Couette Flow and Non-Linear Electronic Circuits Brett Tomlin, Thomas Olsen, Kristine Callan, Richard Wiener Fractal Dimensions of experimental time series are calculated in terms of Correlation Dimension and Kaplan-Yorke Dimension. Numerical techniques were tested on data from a chaotic non- linear electronic circuit. Long time series were obtained from experiments in a modified Taylor-Couette fluid flow apparatus in both laminar and turbulent flow regimes. The irregular generation of Taylor Vortex Pairs in laminar Taylor-Couette flow with hourglass geometry has previously demonstrated low dimensional chaos.\footnote{ T. Olsen, R. Bjorge, \& R. Wiener, Bull. Am. Phys. Soc. \textbf{47-10}, 76 (2002).} The turbulent flow regime is demonstrated to have a higher, yet finite, dimension. [Preview Abstract] |
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C1.00019: Ongoing Observations and Interpretation of Light Curves of a Eclipsing Binary Star System: 44I-Bootes Kasandra Jorgensen, Satomi Sugaya, Thomas Olsen, Christina Thompson We report results from the last year in a decades long study of the eclipsing binary star system: 44I-Bootes. Light curves, representing the intensity of illumination received from the system over the course of a night were measured. This system has demonstrated a consistent rate of slowing over the last century. In addition, we observe a residual oscillation in the times of eclipse with a 58 year period and a 10 minute amplitude. Possible interpretations of this oscillation will be presented. [Preview Abstract] |
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