Bulletin of the American Physical Society
2006 Four Corners Section of the APS Fall Meeting
Friday–Saturday, October 6–7, 2006; Logan, Utah
Session F1: Poster Session |
Hide Abstracts |
Chair: David Peak, Utah State University Room: Eccles Conference Center Third Floor Hallway, 5:30pm |
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F1.00001: Comparison of Satellite and Ground-Based Data on Polar Mesospheric Clouds Jodie Tvedtnes, Michael Taylor, Matthew DeLand, Mark Zalcik Data from the Solar Backscatter Ultraviolet (SBUV) instruments on the NOAA polar orbit satellites have been analyzed to determine the presence of Polar Mesospheric Clouds (PMCs) over the North American continent for five consecutive years from 2001 through 2005. PMCs are ice clouds that form near the mesopause (80-85 km) during summer months at high latitudes. From the ground, these clouds can be seen during twilight hours as Noctilucent or ``night shinning'' Clouds (NLC) and their occurrence has been growing over the last several decades prompting speculation concerning their role in climate change. For this poster we compare reports of displays seen from the ground over the North American continent primarily by observers participating in the Canadian noctilucent cloud observing network CAN AM with the SBUV satellite data. Our primary goal is to investigate the occurrence and spatial extent of the clouds, as well as to search for unusual low latitude events ($<$50 deg) that have occasionally been seen as far south as Logan, Utah. [Preview Abstract] |
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F1.00002: Seasonal Investigation of Variance in Short Period Mesospheric Wave Structure at Low Latitudes. Hema Karnam, Mike Taylor, Jake Gunther As a part of the Maui-MALT program, the Utah State University Mesospheric Temperature Mapper (MTM) has operated continuously at Maui-Hawaii since November 2001. Over 1000 nights of high quality data on Mesospheric temperatures using the near infra red OH and O$_{2}$ emission layers (centered at 87 and 94 km respectively) have been obtained over the past four years. In this study, we have analyzed data from 2003 (295 nights) to perform an initial investigation of the variance in OH and O$_{2}$ signal in the frequency band corresponding to short period (12 min- 1 hour) . This was done by spectrally filtering the data into selected bands (approximately 1 hour wide). The data have been used to study variability in wave content on a night-to-night as well as a seasonal basis. Short period waves were present throughout the year and indicate no obvious summer to winter difference in wave power. On sporadic nights throughout the year, both OH and O$_{2}$ show remarkable enhancements of wave power (factor of 10). Here, we present the results of this initial study. [Preview Abstract] |
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F1.00003: Investigating the horizontal characteristics of the short-period gravity waves over Bear Lake Observatory, Utah. Deepak Simkhada, Michael Taylor, Robert Stockwell The horizontal characteristics of short-period gravity waves were observed in the OH airglow layer at $\sim$ 87 km during a one year period in 2002 from Bear Lake Observatory, Utah (41.90 N, 11.40 W). These waves typically have short periods (6-15 min) with short horizontal wavelengths (8-35 km) and horizontal phase speeds of (20-65 m/s). All the wave events fall into two groups, bands and ripples. The band structures appear as a train of wave fronts with a horizontal wavelength larger than 15 km and the ripples were small-scale structures with a horizontal wavelength less than 15 km. In summer, most waves propagated towards the N- NE, whereas, in winter, wave propagation directions were towards the NW and SW. The observation suggests that these waves were propagated from the lower atmosphere and filtered in the middle atmosphere by the mean background winds. [Preview Abstract] |
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F1.00004: A Niching Genetic Algorithm For Milne-Eddington Spectral Line Inversions Brian Harker, K. Balasubramaniam, Jan Sojka Stokes profile inversions form a basis for ``measuring'' solar magnetic fields. The High Altitude Observatory (HAO) Milne-Eddington (M-E) spectral line inversions have traditionally been used as initializations to more sophisticated inversion procedures. One such code uses a genetic-algorithm initialization to search the parameter space on a more global scale, in an effort to obtain a good starting guess for a more traditional hill-climbing (e.g. Levenberg-Marquardt) algorithm. A serious drawback to the type of genetic algorithm used is that it has been shown to perform poorly on high-dimensional spaces with multiple optima. A single-component M-E model atmosphere is typically described by about 7 free parameters, indicating a fairly high parameter space dimensionality. Two-component models increase the ability to fit frequently-observed asymmetric spectral lines, at the price of nearly doubling the dimension of the parameter space. Furthermore, spectral lines for large magnetic field strengths and large inclinations are very similar to profiles for weaker field strengths and small inclinations, indicating the potential presence of multiple optima that correspond to very different physical conditions. This poster presents an initial investigation into alleviating these difficulties by incorporating a more sophisticated evolutionary strategy into the SGA, and parallelizing over multiple processors. [Preview Abstract] |
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F1.00005: Polar Crater Deposits as a Probe for Ancient Climate Change on Mars John Armstrong Dynamical studies of the Martian orbit suggest a planet that has undergone extreme orbital change. How has this affected the planet's climate? Is there a record of this orbit-induced climate change written in the geology that is expressed on the surface? If so, such a record would provide insight into Mars' climate history, and shed light on the types of habitats for life that may have existed in the past. We are exploring how the current seasonal polar caps interact with polar craters in an effort to identify modification that can be linked to the proximity of the polar cap. Ice deposits within the craters are evident in both thermal spectra and imagery from Mars orbiters. We have linked these ice deposits to morphological deposits that can be identified in other craters that are further from the pole. These deposits may act as a probe of the variations suggested by orbital calculations, as well as provide an indicator of the extent of the sub-surface ice table. We will present preliminary results from a sample of northern craters, and explain how this can be extended to southern craters, and possibly mid-latitude craters, in an effort to understand more fully the martian climate through time. [Preview Abstract] |
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F1.00006: Green Thumbs for the Red Planet Jacque Jackson, David Allred, Niki Brimhall In the famous book, The Case for Mars, Robert Zubrin discusses how resources readily available on Mars could easily be used to construct a greenhouse. This project tests his proposition that plants can be grown in Mars-ambient levels of carbon dioxide. Previous tests have shown that it is possible for plants that have been growing under normal conditions can survive for a period of time in Mars-ambient levels of carbon dioxide, but it has not yet been tested exactly how long they can live under such conditions, nor whether they can be planted and grown in such conditions. We also propose an excellent candidate for a Martian greenhouse plant, namely a Bolivian grain called quinoa. Quinoa is efficient because the entire plant's leaves, root, stem, and fruit are edible and nutritious. Also, quinoa is promising because it is a robust plant accustomed to low pressures and cold temperatures. If it proves possible to grow and cultivate plants in Mars-ambient levels of carbon dioxide, future exploration of Mars would be greatly benefited. [Preview Abstract] |
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F1.00007: Exploring ``Freeze Out'' on Mars using an Atmospheric Circulation Model Michael Esquivel In addition to observational research, computational models like the NASA Ames Mars General Circulation Model (GCM) are used for efficient and often detailed representations of physical quantities. Using this GCM model, I am studying the effects of the distribution and density of frozen carbon-dioxide located at the polar caps. I have paid attention to the effects of the resulting ground temperature, surface pressure, and ground ice through time-based 2D and 3D animations. Also, I have modified the planet's axis between 5 and 50 degrees, changed the pressure by orders of magnitude from zero to two magnitudes, and studied conditions that result to a time frame of nearly 4 billion years ago. Preliminary results show that low pressures with low degrees of tilt have resulting pressures that approach zero, often ending simulations early. The remaining frozen carbon-dioxide remains airborne which could explain the possibility of an atmospheric phenomenon called a ``freeze out.'' This type of atmospheric computational data is often tedious and cumbersome to interface between numerical data and visual format. To counteract this problem, I have built an interface using IDL to interact with raw Mars GCM data. This interface allows researchers to increase the time to study actual science and minimize the time to find and decipher data to a visual format. This interface allows modification of initial variables to allow for cold starts of the Mars GCM model as well as create new maps and view them in an animation sequence to study changes in time. [Preview Abstract] |
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F1.00008: Generalized Stationary States for Plasmas with Conserved Global Helicities A. Kullberg, E.D. Held, W.F. Edwards After decades of work on the subject of minimum energy states for plasmas, a novel theory\footnote{W. F.\ Edwards and E. D.\ Held, {\em Phys. Rev. Lett.,} {\bf 11}, 255001 (2004)} has been developed which includes all of the terms in the energy integral and adjoins local constraint equations that avoid the common assumption of quasineutrality. In order to verify the predictions of this theory as well as extend it to toroidal geometry, we present complimentary work that constrains the variation of total plasma energy under the assumption of conserved global helicities. The resultant Euler-Lagrange equations take the form of coupled, nonlinear partial differential equations for the magnetic and electric fields, plasma flows and densities and the Lagrangian multipliers associated with conserved global helicities. Assumptions regarding symmetry are then employed to convert the Euler-Lagrange equations to coupled ordinary differential equations which are solved using finite-difference, relaxation techniques. Quantitative comparisons of the solutions from these theories are made for the problems of diamagnetism in slab geometry, which is relevant to space plasma in the Venus ionosphere, and cylindrical screw pinches, which is relevant to the confinement of fusion plasmas in the laboratory. Preliminary work regarding minimum energy states in toroidal geometry is also presented. [Preview Abstract] |
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F1.00009: Experimental Verification of a new Plasma Equilibrium State Jeremy Bishop, Ajay Singh, Farrell Edwards, Eric Held It has been shown that a ``steady state equilibria of two-species collisionless plasmas have been found for symmetrical systems by varying the total energy subject to Maxwell's equations, momentum moment equations, and adiabatic equations of state, without imposing a quasineutrality condition''\footnote{W.F. Edwards and E.D. Held PRL \textbf{93}, 255001 (2004)} We have undertaken the task of experimentally verifying that these equilibria exist. In order to do this we have received delivery of equipment from the University of Saskatchewan, consisting of the the components of the tokamak STOR -- 1M. After restoration to working condition, we will modify the equipment to encourage the formation of the equilibrium state. Additional testing will be used to determine feasibility to applications such as neutron and/or power generation. Currently, we are in final preparation for vacuum testing, after which we will complete restoration of the electrical system including capacitor testing,a new optically isolated control system and installing required diagnostics. This will allow us to have first plasma in December 2006. [Preview Abstract] |
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F1.00010: Phi Meson as Probe for Quark Gluon Phase Transition Z. Yasin Vector mesons provides crucial direct signals for characterization of the early times of the quark gluon phase transition predicted at temperature around 150 MeV. Since, Phi Meson is not masked behind other resonances in mass spectra so it provides a nice probe to verify the standard model prediction of chiral symmetry restoration, expected to cause modification of its mass, width and decay channels in the dense hadronic matter. Creation of such a state of matter is main objective of current series of ultra-relativistic heavy ion collision experiments at Brookhaven National Laboratory. Monte Carlo simulations can be used for tracking charge particles through complex detectors. Results from a Monte Carlo Carlo simulation code, developed for verifying the QCD phase transition signals for Phi Meson, will be presented. [Preview Abstract] |
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F1.00011: The Equation of State of $\alpha $-Uranium from a First Principles Perspective Sourav Adak, Boris Kiefer Uranium occurs in diverse environments, for example as a fuel in nuclear reactors and as a major source for the internal heating of our planet. Therefore the understanding of the electronic structure of uranium is important to develop a unified model for uranium in different bonding environments. Heavy elements at the bottom of the periodic table pose a large challenge to theory due to the often complex interplay of s-, d-, and f-electrons that are difficult to treat self-consistently in density functional theory. Here we adopt the simplest description that neglects spin-orbit coupling and any special treatment of strong electronic correlations. The calculations are based on the projected augmented wave method within the GGA approximation. We find that the equation of state is in good agreement with experiment. This suggests that our simplified electronic structure model of uranium captures most of the physics and may be used to describe bonding of this element in other environments at least to first order. [Preview Abstract] |
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F1.00012: Roughness Contributions to Thin-Film Reflectance Elise Martin, Jedediah Johnson, R. Steven Turley In order to find a factor to account for how surface roughness affects reflection and transmission measurements of thin films, we developed a MATLAB program that computes scattering from a rough surface with arbitrary-good accuracy. S-polarized plane waves are reflected off of a perfectly conducting surface with a certain amount of roughness and normalized with reflection from a perfectly smooth surface. In order to best model the kinds of roughness we anticipate in actual thin films, the surfaces were created with cubic splines where the spacing of the knots was varied to control the spatial frequency. The heights of the knots had a random Gaussian distribution. To make these computations useful for extracting index of refraction data from thin-film reflectance measurements, we have developed efficient approximations of the exact calculations that can be used in data fitting programs. These approximations give the roughness correction as a function of incident angle, root-mean-square roughness, and spatial frequency. [Preview Abstract] |
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F1.00013: Time-Space analysis on spreading processes in small-world networks Lin Xue, Zhihuai Zhu, Qi Zhang, Peng Zhang We used time-domain statistical analysis to study the spreading processes on one-dimensional small-world networks. The relationships between the saturated infection rate and both spatial and temporal parameters of the system were studied. We found that the saturated infection rate increase exponentially with the mean degree and linearly with the ratio of the shorts cuts while it is almost independent of the size of the network when the network is large enough, which could not be observed without considering the spatial structure of the model. The infection probability and the active period also influence the saturated infection rate. The obtained results may provide insights into a prognosis of a spreading process in closed system especially for epidemic control. [Preview Abstract] |
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F1.00014: Using Linear Delta Expansion for the Solution of the Schr\"{o}dinger Equation Luis M. Sandoval, Jorge A. Lopez In this work, we present a solution to the Schr\"{o}dinger equation using a method known as Linear Delta Expansion (LDE). The method utilizes different scaling behavior that is found at different distances. In particular, we can identify three ranges of scaling behavior, which can be solved independently. At large distances, we observe an asymptotic behavior that depends only on the form of the potential. The intermediate scale is based also in exponential decay of the wave function. Finally, for short distances, the wave function is sizable. We used this method to solve the quantum anharmonic oscillator, and we obtained good results employing only algebraic equations. [Preview Abstract] |
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F1.00015: Reconstructing Systems of Nonlinear Differential Equations from Time Series Keith H. Warnick, Charles R. Tolle Appropriately modeling a dynamical system by the construction of differential equations is a vital and common task in computational physics. However, generating an acceptable model of the underlying dynamics may be a complex problem in systems which exhibit high-order or nonlinear behavior. This poster details the reproduction and performance of a trajectory method proposed by Perona et al. for the construction of a system of nonlinear differential equations from time series data. By numerically integrating a given set of basis functions, the method uses an iterative algorithm to fit a polynomial in the chosen basis functions to the time series. By this method, time series data from any sufficiently connected and observable system may potentially be used to numerically approximate the equations which give rise to the system dynamics. The demonstrated generality and effectiveness of this method make it a potentially powerful tool for the study of dynamical systems. [Preview Abstract] |
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F1.00016: A thermal beam calcium matter-wave interferometer Jeremiah Birrell, Dan Christensen, Christopher Erickson, Justin Paul, Rebecca Tang, Dallin Durfee We report on progress toward a calcium-beam atom interferometer. The design uses a novel alignment scheme using precision prisms which will cause first-order Doppler shifts to cancel out to high accuracy. The device will utilize a thermal beam of atoms for simplicity and high signals. The atom waves will be split and recombined using a single-photon transition at a wavelength of 657 nm. We are currently working to improve the linewidth of the 657 nm laser and constructing a 423 nm blue laser to transversely cool the atoms and to detect the output of the interferometer. We are also characterizing a thermal Ca beam using laser absorption and working on precise control of the temperature and flux of the beam. [Preview Abstract] |
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F1.00017: Study of Adsorption Isotherms Using Micromachined Quartz Crystal Gravimetric Sensors Jay Mathews, Abhijat Goyal, Srinivas Tadigadapa Using microfabrication techniques, it is possible to realize gravimetric sensor platforms which can resolve mass down to a few femtograms and are robust enough to operate even in aqueous ambient. In this study, an ultra-sensitive quartz crystal microbalance (QCM) was used to study the self-assembly of thiol-based alkyl molecules on the gold electrode of the QCM and subsequent specific adsorption of protein molecules on top of the grown Self Assembled Monolayers (SAMs). Specifically, isotherms for formation of monolayers of 1-hexadecanethiol were generated, as well as adsorption isotherms for proteins such as human serum albumin (HSA) on the grown monolayers. Such fundamental studies using gravimetric sensor platforms with unprecedented sensitivity are expected to result in better understanding of the biological processes in the human body, better control over the self-assembly process, and possibly in realizing a System on a Chip (SOC) entirely through the self-assembly process. [Preview Abstract] |
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F1.00018: Velocity measurements of hohlraum-driven beryllium ``flyer'' plates T. Tierney, J. Cobble, N. Hoffman, B. Devolder In indirectly-driven fusion experiments, energy-coupling between a laser-driven cylindrical hohlraum and the fuel-containing ablator material governs the maximum attainable yield. In the case of the National Ignition Facility, a class of capsules uses copper-doped beryllium ablators containing deuterium-tritium fuel to absorb in excess of 100 kJ of soft x-rays and would hypothetically achieve fusion ignition. In these experiments, planar 0.9\% copper-doped beryllium slabs are mounted on one axial end of a 1.6-mm diameter, 1.2-mm long cylindrical hohlraum. The hohlraum is driven with $\sim$4 kJ of laser energy to radiation temperatures near 150 eV with a 6-ns drive. Bulk hydrodynamic motion of the slab, induced by radiative drive, is measured using side-on x-ray imaging. The slabs' velocities provide estimates of the time-integrated energy received by the beryllium. We present the experimental design and initial results. [Preview Abstract] |
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F1.00019: Instrumentation for Measuring Radiation Induced Conductivity of Insulating Materials Joshua Hodges, J. Corbridge, J.R. Dennison, R.C. Hoffmann, J. Abbott, A. Hunt, R. Spaulding We report on new instrumentation to measure Radiation Induced Conductivity (RIC). RIC occurs when incident ionizing radiation deposits energy in a material and excites electrons into the conduction band of insulators. Conductivity is determined by measuring the current through the thin film samples in a parallel-plate geometry under a constant applied voltage. RIC is calculated as the difference in the equilibrium sample conductivity under no incident radiation and sample conductivity under an incident flux. An accelerator beam at the Idaho Accelerator Center provides the 2-5 MeV incident flux over a range of 10$^{-2}$ to 10$^{+1}$ rad/sec. Measurements are taken simultaneously from 10 large thin film samples (90 cm$^{2}$). Radiation passes through a 4 mm thick stainless steel window that is used to provide a vacuum environment to prevent arcing and contamination. Detail of the instrumentation and preliminary results will be presented. [Preview Abstract] |
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F1.00020: Measurements of the Radiation Induced Conductivity of Insulating Polymeric Materials for the James Webb Space Telescope J. Corbridge, J.R. Dennison, J. Hodges, R.C. Hoffmann, J. Abbott, A. Hunt, R. Spaulding We report on initial measurements of \textit{Radiation Induced Conductivity (RIC)} for twelve thin film polymer materials that are used in the cabling of the James Webb Space Telescope. Results will be used to model possible detrimental arching due to space craft charging effects. RIC occurs when incident ionizing radiation deposits energy in a material and excites electrons into the conduction band of insulators. RIC is determined using a constant voltage test method as the difference in the equilibrium sample conductivity under no incident radiation and sample conductivity under an incident flux. An accelerator beam at the Idaho Accelerator Center provides the 2-5 MeV incident flux over a range of 10$^2$ to 10$^{+1}$ rad/sec. Measurements are made for a range of applied voltages and radiation dose rates. [Preview Abstract] |
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F1.00021: Effects of Fluence and Charge Density for Pulsed, Low-Fluence Measurements of Electron Emission in Highly Insulating Materials Ryan Hoffmann, J.R. Dennison Accurate measurements of the electron emission properties of extreme insulators require highly controlled experimental techniques. Due to the poor electron mobility in insulators, charge can accumulate which will affect future incident and secondary electrons; subsequently, the electron yield will evolve. This evolution is the prime difficulty in measuring the electron yield of insulators. Minimizing the charge in the electron probe using a pulsed, low-current electron beam will largely mitigate these effects. However, to accurately measure the insulator secondary and backscattered electron yields, careful control is required of the beam current magnitude and spatial charge density. Methods for accurately determining pulsed electron beam fluence and charge density profiles will be discussed. The effects on the yield, emission spectra and yield decay curves---as dose per unit area is varied---will also be presented. [Preview Abstract] |
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F1.00022: Dynamics of high frequency magnetization reversal in nanomagnets Zhihuai Zhu The magnetization reversal of two-dimensional nanomagnets driven by high frequency magnetic field is investigated by numerically solving the Landau-Lifshitz-Gilbert equation. It is observed that the hysteresis dispersion, i.e. hysteresis area A as a function of f, exhibits the second resonance once the in-plane effective field is nonzero. The dynamics of this resonance shows some chaotic behaviors, and originates from the transition between the steady state with a small precessional oscillation and a metastable state with a large-angle reversal. Over the high f range, the loop area A for a fixed f oscillates with time t and each component of magnetization shows a periodic maximal reversal. The oscillation of A(t) relates to that coexistences of precessional modes alternately appears in the systemic configuration. Finally, large domains and a size effect on A(t) also are exhibited under a strong exchange interaction. [Preview Abstract] |
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F1.00023: Electrical properties of nanocrystalline ZrO$_{2}$ at high-pressure Anna Trefilova It is shown, that the materials are received from nanocrystallite zirconium oxide have the different properties from bulk material. The combination of external compression and the contribution of a surface create an opportunity of occurrence of the unusual physical and chemical and electrophysical phenomena. Research of such effects is necessary for development of fundamental bases of creation new materials with special properties. We studied correlation between the sizes of crystallite and resistance ZrO$_{2}$ at the pressures 22 - 50 GPa and temperatures 77 - 400 K. The dc resistance measurements were carried out in a diamond anvil cell rounded cone-plane type. We found that the transition pressure of ZrO$_{2}$ depends on crystallite size. The smaller crystals, the smaller transition pressure. The reduction of transition pressure was observed to 10 nm. However at 10 nm the transition pressure rises steeply. It is possible to suspect, that the surface effects essentially change ZrO$_{2}$ conductivity mechanism at high pressures. We studied relaxation processes in ZrO$_{2}$ under the high pressures and the room temperature. The analysis of experimental data has shown that the time function of electric resistance most precisely described by exponential function. It can be seen, that relaxation times depend on pressure and crystallite size. [Preview Abstract] |
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F1.00024: Electrical resistivity measurements of the chalcogenide spinel, CuIr$_{2}$S$_{4}$, under extreme conditions Mark Hanni Electrical resistivity as a function of pressure will be investigated for the thiospinel compound, CuIr$_{2}$S$_{4, }$which exhibits a metal to insulator transition at high pressures. This study will corroborate existing experimental and theoretical work and is the first of its kind to perform high pressure electrical conductivity and insulating phase optical studies in the range of room temperature to liquid nitrogen temperature. In addition, the transport properties of adamantine semiconductors will be studied at high pressure. The resistivity measurements will be made using a pseudo four-wire probing technique, using an AC constant current source, to eliminate thermal noise in the connections, and a nanovoltmeter. The study is currently ongoing and results are still pending. Improvements made to a stepper motor control program and changes to the system used for optical studies will be presented. [Preview Abstract] |
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F1.00025: Ultrasonic studies of Ti-Zr-Ni Quasicrystals Truman Wilson, Dennis Agosta, Robert Leisure Quasicrystalline materials lack the translational periodicity of ordinary crystals, yet are highly ordered. In particular, they have rotational symmetries forbidden for crystals made of repeating unit cells. Much is unknown about the structure and interatomic interactions of these materials. Elastic constants are sensitive to both the local structure and the interatomic potentials. Resonant ultrasound spectroscopy was used to study Ti$_{39.5}$Zr$_{39.5}$Ni$_{21}$ quasicrystals. In this technique the vibrational eigenmodes of small parallelepipeds are excited and analyzed to determine elastic constants and ultrasonic loss. The experiments were carried out over the temperature range of 3 -- 500 K. The bulk, shear, and Young's moduli, as well as Poisson's ratio were determined. The ultrasonic loss was also studied. The temperature dependence of the elastic constants resembles that of ordinary metals, approaching 0 K with zero slope, and becoming linearly dependent on temperature at higher temperatures. The ultrasonic loss shows a broad peak centered near room temperature, which may be associated with phason flips. [Preview Abstract] |
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F1.00026: Making an ultrastable diode laser James Archibald, Matt Washburn, Marshall van Zijll, Christopher Erickson, Brian Neyenhuis, Greg Doermann, Dallin Durfee We have constructed a 657nm diode laser with excellent stability for use in an atom interferometer. The laser is a grating-stabilized diode laser is locked to a high-finesse cavity using the Pound-Drever-Hall method. We have measured a linewidth of about 1 kHz and are working on several improvements which should further reduce our linewidth. [Preview Abstract] |
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F1.00027: Study on energetics of self-assembled quantum dot using molecular beam epitaxy and \textit{in-situ} scanning tunneling microscopy Richard Wilson, Dong Jun Kim, Addison Everett, Haeyeon Yang A chain of quantum dots were observed to form during an annealing process. Strained but flat InGaAs epilayers were grown on nominal (001) surfaces of GaAs substrate by molecular beam epitaxy (MBE) at low temperature below 400\r{ }C. Real-time reflection high energy electron diffraction observations suggest that the strained surfaces are crystalline during deposition processes.\textit{ In-situ} scanning tunneling microscope (STM) shows that the strained surfaces are atomically flat and the surface reconstruction are mixed with various structures. Upon heating the STM observed samples above 450 \r{ }C under arsenic pressure, the strained layers undergo roughening transition, resulting in nanodots. The size and shape of dots depend on the annealing temperature and strain amount. Furthermore, the dots are aligned along straight lines, forming chains of dots. [Preview Abstract] |
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F1.00028: Quantum Dot Modulators Brendan Turner, Manish Mehta, Ramesh Laghumavarapu, Diana Huffaker Mach-zender devices are an ideal modulation source for communication networks at 1.3 $\mu$m and 1.55 $\mu$m. Superlinear electro-optical effects are a desirable feature in mach-zender modulators since their large second order electro-optical coefficient would give complete signal extinction at a small voltage. Quantum dot devices show promise for such applications in the 1.3 $\mu$m band. In this project we performed free-space characterization of stacked InAs quantum dot devices. A crossed polarizer and analyzer combination were used to determine the phase retardation/voltage relation and electro-optical coefficients for said materials. We used different pump wavelengths to analyze their effect on modulation. Further calculations were carried out to determine the theoretical extinction ratio of such devices as part of a mach-zender modulator. [Preview Abstract] |
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F1.00029: One dimensional array of QDs for a single InGaAs layer deposition on a smooth (001) surface of GaAs substrate Joseph Abel, Dong Jun Kim, Addison Everett, Haeyeon Yang The formations of quantum dot arrays during the growth of InGaAs/GaAs were reported using multiple layers or high index on the GaAs substrates. The lateral orderings are formed on the capping layer with reduced lateral strain. The other types of arrays were shown by surface diffusion from the substrates at a corrugated surface, such as the edge of terrace. In this study, we directly suggest one-dimensional array on a flat surface of single layer deposition. The sample growth process was performed by molecular beam epitaxy, which connects to a scanning microscope. A 1$\mu $m thickness buffer was grown at 580\r{ }C to get a flat surface. The surface condition was checked by RHEED. In$_{0.4}$Ga$_{0.6}$As on GaAs (001) substrate was grown at 500\r{ }C with higher arsenic flux than GaAs substrate structure transition amount. The topographic properties of the grown samples were characterized by in-situ STM. Each growth has different InGaAs thickness, from 7.5ML to 6.1ML. In conclusion, we have proposed the new model of InGaAs dot arrays on the GaAs(001) surfaces. Some assumption will be discussed on more experimental results. [Preview Abstract] |
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F1.00030: Crystal structures of Th(Cu,Sn) compounds Farzana Nasreen, Luis M. Sandoval, Karunakar Khotapalli, Alexandre V. Andreev, Heinz Nakotte Powderized samples of Th(Cu,Sn) with nominal compositions of 1:1:1 and 1:2:2 were studied by neutron diffraction techniques using the NPD diffractometer at the Los Alamos Neutron Science Center. The structural analysis of the diffraction data was done using the Rietveld refinement package GSAS, which was developed at Los Alamos National Laboratory. For ThCuSn, assuming an orthorhombic structure with P21cn space group fits the neutron-diffraction data best. We still observed some unindexed reflection, which could be attributed to thorium dioxide as the second phase. The second sample was thought to be ThCu2Sn2, which crystallizes in the tetragonal P4/nmm phase. A careful analysis of the intensities revealed that not all of the Cu positions for this composition are occupied and that the actual composition of our second sample is closer to 1:1.5:2. A similar observation was reported for the magnetic analog UCu2Sn2. [Preview Abstract] |
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F1.00031: Production and Examination of Nanocrystalline Copper Jennifer Albretsen, James Hanna, Qi Zeng, Ian Baker 325-mesh copper powder was ball milled under various conditions to produce copper samples of different grain sizes. One well-milled sample was annealed at varying temperatures and for different times to promote grain growth. These two procedures provide a range of grain sizes for study. Crystallite size was determined by analyzing x-ray diffraction peak broadening. Continuing research would include equal channel angular extrusion (ECAE) of the samples in an attempt to produce bulk nanocrystalline copper, allowing researchers to more easily determine the mechanical properties of this nanocrystalline metal. [Preview Abstract] |
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F1.00032: Toward single Ba or Ba$^{+}$ detection on a fiberoptic tip Shon Cook In progressing toward Ba and Ba$^{+}$ single atom tagging in solid Xe, an efficient laser delivery and fluorescence detection system is needed. One method is the use of an optical fiber for delivery of the laser beam and the same or a different fiber for collection of the fluorescence. Various designs and requirements for accomplishing single atom or ion detection are discussed and initial measurements of scattered light in the fiber(s) are presented. Single atom detection is a reasonable expectation. [Preview Abstract] |
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F1.00033: Temperature Calibration for Sample Heating in Ultrahigh Vacuum Heidi Wheelwright, T.C. Shen Precision temperature measurement is a challenge for ultrahigh vacuum sample preparations. Thermocouples and pyrometers can be used to measure the temperature of samples, but these two techniques need calibration. We have made a mathematical model to calibrate the thermocouple readings with the pyrometer readings. This model is based on equations considering the input power and the heat loss by conduction and radiation. The heat conduction constant is determined from pyrometer temperature measurements at various power inputs. Given any input power, this model will return a temperature value that agrees very closely to the thermocouple readings which have been calibrated with the pyrometer. [Preview Abstract] |
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F1.00034: A Temperature-driven Liquid Xenon Recirculation and Purification System Julio Cesar Benitez-Medina, Kendy Hall We have built a liquid xenon recirculation and purification system in order to address the problem of inconsistencies in our Ba$^{+}$ fluorescence spectra. In our previous work our liquid xenon purity system did not include recirculation, and the liquid xenon contained ppm of electronegative impurities. By continuous recirculation through a getter purifier, ppb purity is expected. Our recirculation system is driven thermally, by applying heat to the evaporation region, instead of by the pump method used by others. The advantage of thermal driven recirculation is that there are no pressure surges. Therefore, the liquid is calm as it evaporates and condenses. This gives excellent optical quality for Ba$^{+}$ spectroscopy in liquid xenon. The goal of this work is to detect fluorescence from single Ba$^{+}$ daughter ions in the Enriched Xenon Observatory (EXO) double beta decay experiment. [Preview Abstract] |
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F1.00035: Phases of Ultra Cold Gases in the Fermi-Bose Hubbard Model Daniel Schirmer The experimental realization of a BEC has stimulated the interest in theoretical models of zero-temperature quantum phase transitions. Ultra cold gases confined in optical lattices can demonstrate a wide range of different phases by varying controllable system parameters, such as optical lattice intensity, particle number, spin composition and the inter-atomic interaction. This project aims to unveil phases in a one dimensional system of fermions coupled to a bosonic molecular state, in the limit of an infinite number of lattice sites. This is accomplished by solving the Fermi-Bose Hubbard model using a numerical method developed by G. Vidal [G. Vidal, Phys. Rev. Lett. 91, 147902 (2003)], and implemented into a Mathematica package by J. E. Williams at NIST, which was used extensively in my research. This research focuses on calculating diagrams of the homogeneous system as functions of nearest neighbor hopping energies, onsite fermion chemical potential, onsite fermi-bose coupling strength, and a detuning factor, determining relative boson chemical potential. For most calculations, onsite interactions are not considered. Because ultra cold gases are possible to create, manipulate, and observe, they function as a future test bed for studies in solid-state physics and quantum computation. Theoretical tools such as phase diagrams are especially important to the development of these fields. [Preview Abstract] |
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F1.00036: Searching for Tertiary Companions to Eclipsing Binary Systems in the LMC Michael Malmrose, Stacy Palen We use a new method to search for possible tertiary companions to EB's in the MaCHO database.~By binning the light-curve data and averaging the magnitude, we derive an average light curve by linear interpolation.~This curve is directly compared to the observed data.~The O-C phase is determined by subtracting the phase of a data point from the phase when the average curve has the same magnitude.~This is done for both the primary and secondary eclipses.~The O-C data are then plotted as a function of time.~We use a Lomb periodogram to search the O-C data for high power signatures in a range of frequencies, yielding periods of possible tertiary companions.~We phase-fold the O-C data obtained from both red and blue filters.~We currently observe the signature sinusoidal variations of a tertiary companion in two systems for both wavelengths.~We suspect that these two objects are stellar in nature. [Preview Abstract] |
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F1.00037: Chemical Patterning by Mechanical Removal of Aqueous Polymers Katherine Barnett, Jodi Knoebel, Robert C. Davis We are developing a new method for micro and nanoscale patterning of lipids and proteins on solid surfaces. A layer of polyethylene glycol (PEG) teminated polyallyl amine (PAA) was initially applied to a mica surface. The PEG surface is a low adhesion surface for proteins. Following polymer deposition an Atomic Force Microscope (AFM) tip was used to remove the polymer layer in desired regions. AFM imaging of the surface after mechanical polymer removal shows squares of exposed MICA surrounded by the PEG surface. The clean mica regions are now available for specific adsorption of lipid or protein layers. [Preview Abstract] |
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F1.00038: Spectroscopic Ellipsometry And Variable-Angle XPS Scanning Liz Strein, Amy Grigg, David Allred The extreme ultraviolet portion of the EM spectrum from 10-100 nm is becoming increasingly important in various technological applications. However, the optical constants in this region are not well known and need further determination. This is done by observing the interaction of EUV light with thin metallic films. It is essential that the composition and thickness of the film are well characterized in order to determine the optical constants. Depth profiling and angle resolved x-ray photoelectron spectroscopy (XPS) are used to characterize the composition of the films. The extent of oxidation at the surface of the films is of particular interest. Current research is focused on determining how spectroscopic ellipsometry and variable-angle XPS scans increase understanding of this oxidation. [Preview Abstract] |
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F1.00039: Effects of As$_4$ flux on morphology of InGaAs quantum dots and the critical thickness N. Lambert, E. Addison Everett, Dong Jun Kim, Haeyeon Yang We present a comprehensive in-situ scanning tunneling microscopy (STM) study of InGaAs quantum dots (QDs) on GaAs (001) substrates as a function of arsenic flux using molecular beam epitaxy (MBE). At 500$^{\circ}$C and with all other MBE growth parameters fixed, changes in arsenic flux result in changes in the morphology of InGaAs QDs. Increasing arsenic flux results in decreasing numbers of InGaAs QDs. Reflection high energy electron diffraction patterns taken before the InGaAs deposition show that the surface reconstruction changes as a function of arsenic flux. The arsenic fluxes were kept the same during the subsequent In$_{.4}Ga$_{.6}$As deposition. After the deposition, the MBE grown samples were cooled down to room temperature by turning the growth stage heater off. The samples were then taken into the STM chamber via ultra-high vacuum port. STM images of InGaAs deposition show no dots with high As4 flux, and very high density of dots with low As4 flux. Effects of arsenic flux on the changes in surface reconstruction surface morphology and density of QDs, and the critical thickness to form the self-assembled QDs will be discussed. [Preview Abstract] |
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F1.00040: Infrared Imaging of Transient Luminous Events (1 – 1.5 microns) Over the Mid –Western US and Comparison with their Visible Wavelength Signatures Matt Bailey, Michael J. Taylor, Dominique Pautet, Walter A. Lyons, Steven Cummer As part of a coordinated campaign conducted from Yucca Ridge, Colorado during summer, 2005, four sensitive imaging systems were fielded by Utah State University to investigate the signatures of transient luminous events (TLE's) over a broad spectral range, extending from the near ultra violet (0.35 microns) to infrared wavelengths (1.5 microns). These measurements were made in conjunction with high speed video and electromagnetic observations providing detailed information of the TLE dynamics and their structures. The USU instruments consisted of two Gen 3 Xybion cameras, one filtered to observe N$_2$ first positive emissions (665 nm) while the second observed white light emissions. A third intensified camera with an extended blue response was fitted with a broad band filter to observe the N$_{2^+}$ first negative and N2 second positive emissions (band width, 350 – 475 nm). Novel infrared measurements were made using an InGaAs imaging array operating at video rates. All four cameras had similar fields of view (25$^{\circ}$) and were co-aligned on a single mount with the high speed imager. We discovered that sprites were easily imaged in the infrared spectral range, and over 30 events were captured with the InGaAs camera arising from thunderstorms over the mid-western United States during early July and mid August. This poster presents new measurements of the optical characteristics of TLEs imaged in the infrared spectral range (1-1.5 microns) and an initial comparison with their visible and near UV signatures. [Preview Abstract] |
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