Bulletin of the American Physical Society
Inaugural Fall 2009 Meeting of the Prairie Section of the APS
Volume 54, Number 17
Thursday–Saturday, November 12–14, 2009; Iowa City, Iowa
Session H2: Poster Session (3:30 - 5:15 PM) |
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Room: IMU 243 (Ballroom) |
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H2.00001: Quantum Causality Threshold and Paradoxes Florentin Smarandache In this paper we consider two entangles particles and study all possibilities when both or some of them are immobile, or both or some of them are moving in various directions, and study the causality between them and the paradoxes generated. We define the Causality Threshold of a particle A with respect to another particle B. [Preview Abstract] |
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H2.00002: Initial Results From Project RESUN, A Radio Search For UHE Neutrinos Using The EVLA Theodore Jaeger, Robert Mutel, Kenneth Gayley The origin, composition, and acceleration mechanism of the highest energy cosmic rays all remain mysteries in astrophysics. However, with measurements indicating an attenuation of the cosmic ray flux for energies greater than 10$^{19.6 }$eV, Ultra High Energy (UHE, E $>$ 10$^{18 }$eV) neutrinos may be the only observable indicators of the extreme universe. While the past 20 years have seen numerous experiments aimed at observing these cosmic messengers, no attempts have yielded a detection. In this light, we present the initial results of the Radio EVLA Search for UHE Neutrinos project. RESUN utilizes highly sensitive antennas to monitor the lunar limb for short-duration radio Cerenkov bursts associated with UHE neutrino interactions. With the first 50 hour implementation of the setup described in this paper, we have already improved the lunar-based UHE particle flux upper limit by a factor of 2 for energies greater than 10$^{21}$ eV. A 200 hour observation (beginning September 2009) will achieve as much as a factor of 100 improvement over previous lunar searches, potentially making the first UHE neutrino detection and unraveling the unknown mysteries of intense astrophysical processes. Also discussed is the difference between lunar observations and ongoing Antarctic ice experiments, and how the results from lunar target experiments compare and compliment their terrestrial counterparts. [Preview Abstract] |
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H2.00003: A Possible Explanation For NuTeV's Anomalous Dimuon Events Thomas Alexander, Andrew Alton We consider a model where WIMPs interact with neutrinos to produce dimuon events as a possible explanation of the NuTeV anomalous dimuon events. The NuTeV events show limited sensitivity to the mass of the WIMP but they are sensitive the mass difference between the WIMP and a more massive charged particle. While the cross section revealed by this model is unusually large the model naturally accounts for the asymmetry between the muon's momentums as well as other features of the NuTeV events. [Preview Abstract] |
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H2.00004: A General Search for Undiscovered Particles Using the ATLAS Esteban Fullana Torregrosa, Jason Boomsma, Serguei Chekanov We present a tool to make a comprehensive and generic search for deviations from the Standard Model in the ATLAS detector at the LHC. The search is based on the invariant mass and the sum of the Pt of the input objects. The program runs over ROOT ntuples and it is fully configurable in terms of input particles (up to six), selection cuts and output histograms. We present the results of successfully running the tool over several physics MC samples and several types of input objects including missing Et, jets, electrons, photons, muon and Z bosons. [Preview Abstract] |
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H2.00005: Cosmic muon analysis in the ATLAS detector Maria Belen Salvachua Ferrando, Nathan Gardner, Rikutaro Yoshida We present a study of the muon to electron response in the Tile calorimeter of the ATLAS detector. The result is based on the analysis of 241,000 cosmic muons events in which we compare the energy response from the calorimeter with the momentum difference between the muon spectrometer and the inner detector. The ionization energy measurement as function of the momentum of the incoming muon is compared with the Bethe-Block prediction; the results show a good a correlation between the calorimeter response and the difference between the measured momentum after and before the calorimeter. [Preview Abstract] |
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H2.00006: Galactic Rotation withOUT Dark Matter: Solar System Perspective Chuck Gallo, James Feng Planetary rotation around our Sun is described with Newtonian gravity/dynamics. These two-body calculations balance gravitational and centrifugal forces to yield stable orbits. The rotation of disk galaxies involves the gravitational interaction of many bodies, but this data is also described with Newtonian gravity/dynamics by balancing all the gravitational forces against the centrifugal forces at each and every point in the galactic disk to yield stable rotation. A thin-disk galaxy is complex mathematical problem that does NOT have an analytical solution. Numerical (computational) techniques are required to obtain an accurate UNIQUE STABLE solution for the radial mass distribution to yield any specific measured rotation curve. Both the Solar and Galactic rotation descriptions are achieved withOUT Mysterious Dark Matter which has never been experimentally detected. Speculations re Dark Matter are NOT required to describe the galactic rotation curves and achieve stability, only Newtonian physics with numerical solutions enabled by modern computational techniques.\\[4pt] References:\\[0pt] http://arxiv.org/abs/astro-ph/0803.0556\\[0pt] http://arxiv.org/abs/astro-ph/0804.0217\\[0pt] http://arxiv.org/abs/astro-ph/0804.3203 [Preview Abstract] |
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H2.00007: The Gravity and Extreme Magnetism Small Explorer (GEMS) Philip Kaaret, Jean Swank, Keith Jahoda, Tim Kallman The Gravity and Extreme Magnetism Small explorer (GEMS) was recently selected for flight in 2014 by NASA and will make the first sensitive search for X-ray polarization across a wide set of source classes including stellar black holes, Seyfert galaxies and quasars, blazars, rotation and accretion-powered pulsars, magnetars, shell supernova remnants and pulsar wind nebulae. GEMS will observe 35 targets during the 9 month prime mission. A possible science enhancement option would extend the mission with a 15 month guest observer phase. GEMS is implemented using time projection chamber (TPC) polarimeters with high efficiency in the 2-10 keV band behind thin foil mirrors. It also allows a small Bragg reflection soft X-ray experiment to be included that can extend the sensitivity to 0.5 keV. The entire spacecraft, less the solar panels, is rotated to enable measurement and correction of systematic errors. We will discuss the design of GEMS and the planned science program. [Preview Abstract] |
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H2.00008: The Student Experiment on the GEMS Mission Ryan Allured, Philip Kaaret, Zachary Prieskorn, Alicia Maxwell The Gravity and Extreme Magnetism Small Explorer (GEMS) is an exciting new mission that will make X-ray polarization measurements of a large number of objects of different classes. The main instrument is sensitive in the 2-10keV band. Students at the University of Iowa are currently building a Bragg Reflection Polarimeter (BRP) that will supplement the main instrument by providing sensitivity at 500eV. The BRP consists of a multilayer crystal reflector, a proportional counter, and electronics. The multilayer crystal will be used to reflect the soft X-rays from the telescope beam to the proportional counter. In addition to having a high reflectivity at 500eV, the reflector must transmit the high-energy X-rays efficiently, so as not to interfere with the main instrument. The proportional counter will use charge division to sense position in one dimension, and will contain anti-coincidence anodes to reject background events. The BRP will make polarization measurements by measuring the intensity of observed radiation as the spacecraft rotates around the telescope axis. The primary use for low energy polarization measurements is to fix the inclination angle of the accretion disks of black holes. [Preview Abstract] |
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H2.00009: Energetics of Non-thermal Accelerated Electrons and Thermal Plasma during Solar Flares Christopher Moore, Brian Dennis Since the beginning of its operation on February 12, 2002, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed numerous solar flares. RHESSI measures the solar flux from 3 keV (soft X-rays) to 17 MeV (gamma rays) with 1 keV spectral resolution. Assuming a thick-target flare model, energy estimations of the non-thermal accelerated electrons and the plasma at the thermal peak can be obtained through spectral and image analysis. This model is composed of an exponential with an average temperature for the thermal component and a single delta power law for the non-thermal component. Energy estimations have been carried out for over 30 flares from solar cycle 24. [Preview Abstract] |
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H2.00010: The Origin of Stellar Rotation Stewart Brekke In the early universe stellar cores were formed primarly in the galactic and pre-galactic arms. These cores were made up of a dense hydrogen mass prinarly which were slowly rotating. Orbiting these dense hydrogen cores were dense concentric rings of primarily hydrogen gas moving at a relatively fast rate. As the orbits of the rings decayed due to gravitational attraction, the rings of orbiting hydrogen matter tangentially collided and adhered to the pre-formed stellar core transfering the faster orbital angular momemtum of the rings to the stellar cores resulting in a faster rotating stellar bodies which over time began to rotate differentially due to internal forces from stellar burning. [Preview Abstract] |
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H2.00011: Field-free molecular alignment for studies using x-ray pulses from a synchrotron radiation source Phay Ho, Michelle Miller, Robin Santra A short, intense laser pulse may be employed to create a spatially aligned molecular sample that persists after the laser pulse is over. We theoretically investigate whether this impulsive molecular alignment technique may be exploited for experiments using x-ray pulses from a third-generation synchrotron radiation facility. Using a linear rigid rotor model, the alignment dynamics of model molecular systems with systematically increasing size is calculated utilizing both a quantum density matrix formalism and a classical ensemble method. For each system, the alignment dynamics obtained for a 95-ps laser is compared to that obtained for a 10-ps laser pulse. The average degree of alignment after the laser pulse, as calculated quantum mechanically, increases with the size of the molecule. This effect is quantitatively reproduced by the classical calculations. The average degree of impulsive alignment is high enough to induce a pronounced linear dichroism in resonant x-ray absorption using the intense 100-ps x-ray pulses currently available. However, for structural studies based on elastic x-ray scattering, bright x-ray pulses with a duration of 1 ps or shorter will be required in order to make full use of impulsive molecular alignment. [Preview Abstract] |
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H2.00012: Role of surface band structures in the survival of anions scattered off plane and nano-stepped surfaces Andrew Schmitz, John Shaw, Himadri Chakraborty, Uwe Thumm Resonant charge transfer between ions and metal surfaces is a valuable tool to explore the surface electronic structure. Using the Crank-Nicholson propagation [1] we solve the time-dependent Schroedinger equation to simulate the dynamic electron redistribution during the scattering of a hydrogen anion from plane and nano-stepped vicinal metal surfaces. The electronic evolution during the scattering and the final ion survival probability as a function of the projectile's incident angle are calculated. We find that the survival of the ion reflected from a plane surface is very sensitive to the component of the projectile speed perpendicular to the surface. For a host of simple metal surfaces, unique roles of the band gap and the image states are uncovered that enable a nearly universal energy-scaling of the ion-survival. For the stepped surfaces, conversely, the survival is found to depend critically on the ion speed parallel to the surface, resulting in rich structures in the survival probability.\\[4pt] [1] Chakraborty et al., \textit{Phys. Rev.} A \textbf{70}, 052903 (2004). [Preview Abstract] |
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H2.00013: Decomposition based recovery of absorbers in turbid media Isaac Goodin, Ben Rogers, Q. Su, R. Grobe We suggest that the concept of the point-spread function traditionally used to predict the blurred image pattern of various light sources embedded inside turbid media can be generalized under certain conditions to predict also the presence and location of spatially localized absorbing inhomogeneities based on shadow point spread functions associated with each localized absorber in the medium. The combined image obtained from several absorbers can then be decomposed approximately into the arithmetic sums of these individual shadow point spread functions with suitable weights that can be obtained from multiple regression analysis. This technique permits the reconstruction of the location of absorbers. [Preview Abstract] |
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H2.00014: Monte Carlo simulations of turbid media David Wischhusen, Isaac Goodin, Q. Su, R. Grobe We simulate numerically the propagation of a light beam inside a finite highly scattering medium. The medium is characterized by an absorption coefficient, a scattering coefficient and a phase function. We analyze the spatial distribution of the scattered light at the exit surface of the medium. We then insert various absorbing objects into the medium and study their effect on the scattered light. The data are also used as a basis to examine the validity of the decomposition based imaging scheme to recover the location of the embedded objects. [Preview Abstract] |
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H2.00015: Cooling and Near-equilibrium Dynamics of Atomic Gases across the Superfluid-Mott Insulator Transition Xibo Zhang, Chen-Lung Hung, Nathan Gemelke, Cheng Chin Achieving low enough temperature is necessary for atoms in an optical lattice to probe ground state many-body physics. Experimentally, the lattice potential is gradually ramped up; adiabaticity of the ramp determines the final temperature of the atomic cloud. Here we study the temperature and dynamics of Cesium 133 atoms across the bosonic superfluid (SF) to Mott insulator (MI) transition. We show that lattice ramps developed to ensure only local adiabaticity can yield samples far from global thermal equilibrium. An intriguing local cooling effect is observed during this process. From a finite-temperature density fit derived in the MI regime, we find that temperature can drop significantly at the center of the sample. In addition, the inner and outer temperatures take a long time (over one second) to converge. Possible mechanisms for the local cooling near the cloud center include the Joule-Thomson effect of cooling a Bose gas, as well as locally isentropic cooling due to the vanishing of SF critical temperature near the quantum critical point. Our work provides new prospects to observe novel quantum phases at very low temperature. [Preview Abstract] |
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H2.00016: Training Ultrafast Laser Pulses Ruslan Averin, N. Wells, M. Todt, N. Smolnisky, N. Jastram, B. Jochim, N. Gregerson, E. Wells, A. Sayler, J. McKenna, K. Carnes, I. Ben-Itzhak, M.F. Kling Closed loop control of molecular processes utilizing shaped ultrafast laser pulses has been around for a number of years, yet this type of control has primarily utilized Time of Flight ion yield data for feedback. We present experiments using Velocity Map Imaging (VMI) as the feedback source for the closed loop control. Using VMI allows for pulse optimization not only with respect to the disassociation species but also angular information of the final state. We demonstrate the feasibility of incorporating this kind of feedback into the control loop. Using this technique, we controlled the dissociation branching ratio of CO$^{+}$ into C$^{+ +}$O or C $^{+}$O$^{+}$ and used the VMI information to recover additional information about the control mechanism. [Preview Abstract] |
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H2.00017: Progress Towards Scalable Quantum Manipulation using Two Atomic Species in Independent Optical Lattices Kara Lamb, Arjun Sharma, Peter Scherpelz, Kathy-Anne Brickman Soderberg, Nathan Gemelke, Cheng Chin Advances in quantum information and quantum simulation require novel experimental techniques to provide precise control at the quantum level. One bosonic and one fermionic species of ultra-cold neutral atoms, trapped in overlapping, independently controlled optical lattices offers a promising system for such manipulations. After initial cooling, Pauli exclusion allows fermionic $^{6}$Li to be loaded with high fidelity unit occupancy into one lattice. Bosonic $^{133}$Cs atoms can be loaded with much lower occupancy into a second lattice to act as messenger atoms. By relative translation of the lattices using an electro-optic modulator array, the atomic wavefunctions of a Cs and any given Li atom can be overlapped and entangled through a molecular state. Scalability is inherent since a single Cs atom can be moved between any two distant Li atoms. Our initial studies will focus on interspecies collision properties, which will guide strategies to implement entangling operations. [Preview Abstract] |
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H2.00018: Self Organization in the Solar Corona and Interstellar Medium Steven Spangler Self-organization can be defined as the process by which a physical system, in the course of its evolution, changes its spatial structure, the form of its equations of motions, or key coefficients in those equations. Paradigmatic examples are chemical reactions of the reaction-diffusion type, and biological systems. I discuss astrophysical processes where similar sorts of dynamics may be occurring. The first example is Joule heating of the solar corona. A major problem in astrophysics is the physical mechanism or mechanisms responsible for heating the solar corona to 1-2 million K. Coronal heating by turbulent current sheets is negligible if a standard expression for the resistivity of a plasma is used, but as the current sheets evolve, they develop progressively higher current densities. These high current densities can enhance the resistivity via plasma instabilities, and make Joule heating a more effective process. The second example is from the interstellar medium. The formation of massive stars leads to processes which compress the nearby interstellar medium, making star formation a more efficient process. Similarities and differences with better studied systems exhibiting self organization will be discussed. [Preview Abstract] |
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H2.00019: Numeric Solution of Plasma Impulse Response with Model Fokker-Planck Operator Kristopher Klein, Fred Skiff Using a model Fokker-Planck collision operator\footnote{J. P. Dougherty Phys. Fluids \textbf{7} (1964)} we have investigated the impulse response of a kinetic plasma, in prescribed external electric and magnetic fields, due to several types of perturbations in phase space. The one-dimensional case is treated numerically as a solution of a Fredholm-Volterra Equation of the Second Kind. We also provide motivation for using the same numeric method for finding solutions of the higher dimensional cases. By comparing the numeric impulse response to measured two-point correlation functions in a magnetized plasma, we hope to test Onsager's regression hypothesis. [Preview Abstract] |
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H2.00020: Heating via Kinetic Turbulence in Low Beta Plasmas Jason TenBarge, Gregory Howes Kinetic turbulence provides the mechanism by which large-scale spatial motions are transformed into small-scale fluctuations, which are dissipated via kinetic mechanisms into heat. In magnetized plasmas, the cascade is governed by Alfv\'{e}n waves and is highly anisotropic---the cascade to smaller scales is in the direction perpendicular to the local mean magnetic field. As such, gyrokinetics, in which averages are taken over the gyrophase, is well suited to the study of kinetic turbulence. The gyrokinetic cascade is studied numerically via the simulation code AstroGK, which is based upon a mature code used by the fusion community, GS2. Linear kinetic theory predicts large-scale ion kinetic energy is primarily dissipated as electron heating via a kinetic Alfv\'{e}n wave cascade in low beta plasmas; however, preliminary gyrokinetic simulations of low beta plasmas suggest much of the initial kinetic energy of the ions remains in the ions and provides enhanced ion heating compared to linear theory. The likely mechanism for the observed difference is the inherently nonlinear entropy cascade, which is a turbulent cascade in velocity space. The enhanced ion heating in these gyrokinetic simulations could provide an explanation for the anomalously high temperatures observed in the low beta plasma of the solar corona. [Preview Abstract] |
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H2.00021: Full spin control in 2DEGs with no magnetic fields B.J. Moehlmann, Michael Flatt\'e A properly chosen closed spin transport path in the plane of a III-V semiconductor quantum well suffices for arbitrary spin manipulation of conduction electrons about any desired axis. This feature of spin transport relies on the non-commutativity of the precession matrices associated with non-colinear path segments. The electron spin rotation depends solely on the path geometry, not the speed of the spin along the path. Simple closed paths have been found which will perform arbitrary spin rotations along arbitrary axes with no net spatial displacement of the spins. The paths differ depending on the form of the internal effective magnetic fields induced by crystal asymmetry, growth asymmetry, and strain and electric fields. This work was supported by an ONR MURI. [Preview Abstract] |
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H2.00022: D'yakonov-Perel' spin relaxation in the interacting electron gas in doped semiconductors Matthew Mower, Giovanni Vignale D'yakonov-Perel' spin relaxation is an effect arising from spin precession in spin-orbit split bands, limited by various collision mechanisms. The effect is of fundamental importance to spintronics as it controls spin polarization decay times in semiconductors. We extend previous theoretical calculations of D'yakonov-Perel' spin relaxation based on electron-(electron, impurity, hole, phonon) collisions with a careful analysis of the scattering time due to electron-electron collisions in spin-orbit split bands from a fully microscopic approach under typical low temperature III-V semiconductor conditions for 1, 2, or 3 degrees of freedom. In particular, we make use of the classic Abrikosov-Khalatnikov Fermi liquid approach in the scattering time calculation. Electron-electron scattering times and spin relaxation times are compared to previous work, as well as applied to a recent experimental study on spin polarized electron diffusion in GaAs quantum wells. [Preview Abstract] |
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H2.00023: Aharanov-Casher Effect for Spin Waves in a Ferromagnet Tianyu Liu, Giovanni Vignale Spin dynamics of an electronic system in the presence of spin-orbit interaction is described in terms of the spin-spin response function. Starting from the double-exchange model in a system consisting of one itinerant electron and two localized ions each of which carries a spin 1/2 we calculate the transverse spin response function of the two localized spins and arrive at a first-principle derivation of the Aharanov-Casher effect on the phase of spin waves in ferromagnetic materials. Next we consider a system of classical localized spins embedded in an electron gas (in the weak coupling limit, this reduces to the RKKY model). By solving the coupled equation of motion for the itinerant and localized electron spins in the presence of spin-orbit coupling we obtain the expected quadratic dispersion relation for spin waves in long wave-length approximation: however, the spin-wave momentum is shifted by a spin-dependent factor in the presence of an electric field. This fact indicates that the spin wave in real space will get a corresponding phase factor under the influence of Aharanov-Casher effect. [Preview Abstract] |
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H2.00024: In- and out-of-plane London penetration depths in single crystals of FeSe$_{0.4}$Te$_{0.6}$ superconductor Hyunsoo Kim, Makariy Tanatar, Ryan Gordon, Catalin Martin, Zhiqiang Mao, Ruslan Prozorov In- and out-of-plane London penetration depths $\lambda(T)$ were measured in single crystals of FeSe$_{0.4}$Te$_{0.6}$ superconductor by means of the tunnel diode resonator technique. The penetration depth does not show BCS-like exponential saturation at low temperature. Instead, we found that both $\Delta\lambda_{ab}(T)$ and $\Delta\lambda_{c}(T)$ has nearly quadratic behavior, similar to that observed in the FeAs-based superconductors. We also calculated the in-plane superfluid density $\rho^s(T)=\lambda^2(0)/\lambda^2(T)$, and fitted with various possible models. [Preview Abstract] |
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H2.00025: The Determination of $\lambda _{ab}$(0) in Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ from Tunnel Diode Resonator Measurements Ryan Gordon, Hyunsoo Kim, Catalin Martin, Nicholai Salovich, Ni Ni, Makariy Tanatar, Russell Giannetta, Paul Canfield, Ruslan Prozorov The tunnel diode resonator (TDR) technique allows for precision measurements of the change of the London penetration depth with temperature, $\Delta \lambda $(T), in superconductors, but before now this approach has been insensitive to the zero temperature value, $\lambda $(0), which is necessary for absolute calibration. A method for the determination of $\lambda $(0) in superconductors has been developed that utilizes the capabilities of the TDR system along with a technique in which samples are coated with a thin film of aluminum [1]. Using this procedure, $\lambda _{ab}$(0) has been measured for the Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ series for superconducting samples ranging from underdoped to overdoped concentrations. The resulting temperature dependence of the superfluid density, $\rho _{s }$= [$\lambda $(0)/ $\lambda $(T)]$^{2}$, constructed from penetration depth measurements also obtained using a TDR system, will be discussed in terms of current theoretical models. [1] R. Prozorov \textit{et al.}, Appl. Phys. Lett. \textbf{77}, 25 (2000). [Preview Abstract] |
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H2.00026: Manipulation of Dopants in a Two Dimensional Matrix Timothy Kidd, Laura Strauss, Polina Skirtachenko, Dustin Klein The layered dichalcogenides can be used as a matrix for incorporating and manipulating dopants in dimensionally constrained manner. The crystal structure of the dichalcogenides is formed of two-dimensional strongly bound layers separated by a van der Waals gap. Dopants can be incorporated between the layers as intercalants through a variety of methods to form a semi-ordered phase. These intercalants have a strong impact on the electronic and magnetic properties of the overall system and can be used to tune or enhance novel phase transitions found in the pure parent compounds. Herein, we discuss how one can manipulate the arrangement of dopants using self-assembled and top-down methods to yield a high level of control over the local electronic and magnetic structure of these materials. [Preview Abstract] |
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H2.00027: Determination of polaron hopping frequency limits in modified vanadate and lithium borovanadate glass systems from EPR line-narrowing J. McKnight, K. Whitmore, P. Bunton, S. Feller, D. Vennerberg, B. Baker Electron Paramagnetic Resonance (EPR) spectra of four different vanadate glass systems of varying molar ratios, R, show that the hyperfine structure lines (hfs) become more resolved and defined as R increases. For example, in the sodium oxide vanadate glass system, RNa2OV2O5, low R-values (around 0.1) result in little to no hyperfine resolution in the EPR spectra. However, as the R-value increases and approaches 0.5, the spectra significantly become more resolved, and a dramatic narrowing of the lines occurs, revealing a hyperfine coupling parameter B of order 17.7 mT, corresponding to an upper-limit polaron hopping frequency of 487 $\pm $ 20 MHz. In the model proposed here, this narrowing is due to an increase in hopping time for polarons associated with V4+ ions. By similar analyses, the systems of RCaOV2O5, RBaOV2O5, and RLi2OV2O5 exhibit comparable polaron hopping frequency limits of 480 $\pm $ 20 MHz, 469 $\pm $ 20 MHz, and 468 $\pm $ 20 MHz, respectively, when R is near 1.0. Data taken at various temperatures ranging from room temperature to 4.2 K reveal that EPR spectra linewidths are not dependent upon temperature. [Preview Abstract] |
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H2.00028: Study of the structure and oxygen storage/release capacities of Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$ (0 $\le $ x $\le $ 1) Steven Remsen, Bogdan Dabrowski, Omar Chmaissem, Stanislaw Kolesnik, James Mais Synthesis, oxygen storage/release capacities (OSC), oxygen absorption/desorption rates, and preliminary structural properties of Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$(0 $\le $ x $\le $ 1) have been studied by x-ray and neutron powder diffraction, dilatometry, and thermogravimetric analysis. This system has been found to have excellent reversible OSC at low-temperatures of 200 - 375\r{ }C and oxygen content of these structures have also been found to be sensitive to changes of partial-pressures of oxygen in this low-temperature range, making them potential candidates for oxygen sorbents in novel gas separation methods such as thermal swing absorption and thermal-automatic recovery processes. The OSC of the Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$system relies on the difference in oxygen content of a reversible phase transition between hexagonal P6$_{3}$cm ($\delta $ = 0) and a previously unreported phase of this system ($\delta $ = 0.25, currently under investigation) and pyrochlore Fd3m ($\delta $ = 0.50, Subramanian et al. J. Solid State Chem. 72 (1988) 24). [Preview Abstract] |
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H2.00029: Construction of an Inexpensive Scanning Tunneling Microscope for Undergraduate Laboratories Paul Garcia, Justin Nitz, Mark Plano Clark, Axel Enders Our goal is to produce an inexpensive, room-temperature, atmospheric-pressure scanning tunneling microscope (STM) with atomic resolution. Our prototype uses slip-stick motion for coarse approach to the surface to be imaged. Motion of the tip is accomplished with four flat piezoelectric translators that provide both z-motion (slip-stick and feedback control) as well as the x-y scanning motion. Maximum x-y scan range is estimated and measured to be approximately 1.7 $\mu $m x 1.7 $\mu $m and the fine z-motion range is estimated to be about 570 nm. Control of the x-y motion is done with a microcontroller containing two 16-bit DACs (digital to analog converter). The z-motion is driven by an analog loop that amplifies the tunneling current and then drives the inner electrode of the piezo translators. The cost of our prototype is currently under {\$}300 and we hope to keep it very affordable for high school and college teaching laboratories. [Preview Abstract] |
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H2.00030: Lead Silicate Glasses and Neutron Scattering Gloria Lehr, Adam Vitale, Mario Affatagato, Steve Feller, Alex Hannon, Emma Barney, Diane Holland Lead silicate glasses can be formed with a very large range of lead concentrations. This raises many questions about the structure of the lead silicates. It is believed that at high concentrations, the lead becomes a glass former rather than a modifier. Many studies have been done on lead silicate glasses, and more analysis is being performed to better understand the structure of lead glasses especially at high concentrations. All samples were characterized by their transition temperature and were found to be self-consistent and in accord with the trends from earlier studies. High lead concentration samples were also characterized by x-ray diffraction to ensure that samples were glassy. Samples were successfully made from 33.3 through 80 mol {\%} PbO. These samples are being tested by elastic neutron scattering to further study the complexities of the two glass forming networks PbO and SiO2. [Preview Abstract] |
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H2.00031: Barium Vanadate Microspheres Shari Yosinski, Landon Tweeton, Steve Feller, Mario Affatigato It has been found that many glass powders can form micro- or nanospheres when heated in a flame or by a laser. Much of the research in this area of microspheres has concentrated on making hollow spheres, called microballoons, of silica and borosilicate glasses. Our aim was to create highly porous barium vanadate microspheres for possible future applications in material storage. The surface area of porous spheres would provide a greater amount of bonding surface area for dopants than hollow spheres. Barium vanadate glass with a molar fraction of 0.4 to 0.6 barium oxide was used because this glass is stable and has a low Tg. Size distributions of the spheres were quantified and the extent of sphere formation and porosity was examined using a scanning electron microscope. The size of spheres formed is affected by powder size, dropping method, and flame position. The porosity of the microspheres is affected by flame temperature, time spent in flame, and the material onto which the spheres fall. The greatest porosity was achieved by first heating the glass powder at a low temperature and then immediately sending it through the flames of two MAPP gas torches at approximately 2100$^{\circ}$C onto a metal sheet. [Preview Abstract] |
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H2.00032: EPR Study of Frontally Polymerized Acrylate Polymer Systems A. Thoma, A. Valencia, B. Baker, P. Bunton, J. Pojman, V. Viner Trimethylolpropane trimethacrylate (TMPTMA), 1,6-hexanediol diacrylate (HDODA),and trimethylolpropane triacrylate (TMPTA-n) were frontally polymerized and analyzed via electron paramagnetic resonance (EPR) spectroscopy. A comparison of radical concentration was performed for individual polymers and copolymers. Samples were mapped down the EPR tube to observe behavior of radicals down the polymerization front. During the frontal method, a large spike in intensity is observed at the point of initiation. Within a few centimeters, the signal diminishes into a steady state. As the concentration of TMPTMA was increased linearly in mixtures with TMPTA-n, an exponential growth of the radical concentration was observed. This exponential growth was not observed in the TMPTA-n-HDODA copolymer; increasing the HDODA concentration led to a linear growth of radical concentration. Frontal polymerization was also compared to bulk polymerization. The bulk method produced a larger number of radicals than the frontal method. [Preview Abstract] |
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H2.00033: Comparison of single junction to multiple-quantum well quaternary GaInAsSb 2.2 $\mu $m light-emitting diode Jinhui Tan, Jonathan Olesberg, Lee Murray, John Prineas A strained GaInAsSb/AlGaAsSb multiple-quantum well (MQW) light emitting diode (LED) emitting at 2.2$\mu $m infrared region is investigated. The heterostructure was grown by molecular beam epitaxy and consists of an active region which contains three compressively strained 12nm thick Ga$_{0.64}$In$_{0.36}$As$_{0.06}$Sb$_{0.94}$ QWs separated by 20nm thick Al$_{0.28}$Ga$_{0.72}$As$_{0.02}$Sb$_{0.98}$ barrier in a separate confined heterostructure. X-ray diffraction measurement was used to verify the MQW alloy composition. The sample was processed into variable sized surface emitting LEDs. The emission wavelength was measure with spectrograph and the electroluminescent power (L) was characterized versus current (I) and voltage (V). A peak emission power of 13mW/mm$^{2}$/sr from the 200x200$\mu $m$^{2}$ LED was observed at room temperature with 3000A/cm$^{2}$ peak drive current density at 1{\%} duty cycle. Compared to the single junction bulk LED, the MQW LED exhibited an increase in the output power from 4.5 to 13mW/mm$^{2}$/sr. We will also present the analysis of series resistance and the radiative efficiency of these devices. [Preview Abstract] |
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H2.00034: Excitons in double-walled carbon nanotubes: fluorescent spectrum Barry Yeh The fluorescent spectroscopy of the double-walled carbon nanotudes (DWNT) is mapped to the chirality and diameter feature by the result from single-walled carbon nanotubes (SWNT). The transition energy of SWNT's resonance Raman spectroscopy is applied to categorize DWNT's chirality and diameters relationship [P.T. Araujo et. al, 2007 ]. The agreement of their energy level distribution will decide whether the fluorescent spectrum can be use to distinguish carbon nanotubes and the different activity between SWNT and DWNT. Not a peak contains two chiralities at one data set. Since DWNT contains two SWNTs, tubes where matched up within a diameter difference of 0.67nm $\sim $ 0.77nm [M. Gao et. al, 2005]. [Preview Abstract] |
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H2.00035: Copy number variation and mutation Brian Clark, Jacob Weidner, Kevin Wabick Until very recently, the standard model of DNA included two genes for each trait. This dated model has given way to a model that includes copies of some genes well in excess of the canonical two. Copy number variations in the human genome play critical roles in causing or aggravating a number of syndromes and diseases while providing increased resistance to others. We explore the role of mutation, crossover, inversion, and reproduction in determining copy number variations in a numerical simulation of a population. The numerical model consists of a population of individuals, where each individual is represented by a single strand of DNA with the same number of genes. Each gene is initially assigned to one of two traits. Fitness of the individual is determined by the two most fit genes for trait one, and trait two genetic material is treated as a reservoir of junk DNA. After a sufficient number of generations, during which the genetic distribution is allowed to reach a steady-state, the mean numberof genes per trait and the copy number variation are recorded. Here, we focus on the role of mutation and compare simulation results to theory. [Preview Abstract] |
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H2.00036: Dependence of gene copy number variation on reproductive processes Jacob Weidner, Kevin Wabick, Brian Clark DNA is divided into genes, which are generally thought to come in pairs and code for a trait or part of a trait. Recently, evidence shows that there are multiple copies of a non-trivial number of genes and that the number of copies of some genes varies greatly from individual to individual. The role of fundamental processes including mutation, crossover, and inversion in determining the number of copies of specific genes is not understood. We report on the relationship between these fundamental processes and copy number variation as investigated via a numerical simulation. In the simulation, individuals are modeled by a single strand of DNA consisting of a set number of genes assigned to different traits. Individuals reproduce according to their fitness as calculated with the two most fit genes assigned to one specific trait. [Preview Abstract] |
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H2.00037: Video Analysis of a Plucked String: An Example of Problem-based Learning Christopher D. Wentworth, Eric Buse Problem-based learning is a teaching methodology that grounds learning within the context of solving a real problem. Typically the problem initiates learning of concepts rather than simply being an application of the concept, and students take the lead in identifying what must be developed to solve the problem. Problem-based learning in upper-level physics courses can be challenging, because of the time and financial requirements necessary to generate real data. Here, we present a problem that motivates learning about partial differential equations and their solution in a mathematical methods for physics course. Students study a plucked elastic cord using high speed digital video. After creating video clips of the cord motion under different tensions they are asked to create a mathematical model. Ultimately, students develop and solve a model that includes damping effects that are clearly visible in the videos. The digital video files used in this project are available on the web at \underline {http://physics.doane.edu} . [Preview Abstract] |
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H2.00038: Determination of Particle Shape Distributions of Mineral Dust Aerosols Using Spectroscopic and Light Scattering Measurements Brian Meland, Paula Hudson, Vicki Grassian, Mark Young, Paul Kleiber Atmospheric aerosol play a significant role in the Earth's atmosphere through scattering and absorption of incoming solar radiation as well as outgoing IR terrestrial radiation. Optical remote sensing techniques are often used to estimate aerosol loading, composition, and size distributions. However, these techniques are dependent on an accurate knowledge of the optical properties of the aerosol, which are dependent on the aerosol composition and particle shape. In this work we measure the light scattering phase functions, linear polarizations, and the IR absorption of atmospherically relevant mineral dust aerosol. We explore the possibility of using IR spectral line profiles to infer mineral aerosol particle shape distributions which can then be used in T-Matrix calculations of the phase function and polarization of the scattered light. This has allowed for better agreement with the experimentally measured scattering than was obtained using a more limited range of particle shapes. This research aims to reduce uncertainties in remote sensing measurements by allowing for an independent check of particle shapes. [Preview Abstract] |
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H2.00039: Monte Carlo simulation study of simple two-dimensional systems Michael Hughes The relationship between the two-particle interaction potential in a system and the macroscopic observables that result is a key issue in statistical mechanics. To explore this relationship, Monte Carlo simulations are performed on a variety of two-dimensional systems including hard disks and a 2-D Lennard-Jones system. For hard disks, we were not able to confirm the prediction that there is a phase transition containing a region where the pressure is constant with increasing density, although there is evidence that a solid forms under certain conditions as expected. We are also able to produce a pressure-density plot at a constant temperature for the Lennard-Jones model, which shows evidence of a fluid-solid phase transition around $kT/\epsilon = 0.82$. Also, Monte Carlo calculations are performed directly in the Gibbs ensemble by allowing fluctuations in the volume and particle number, and the phase boundary lines are located more expediently than they are by using traditional canonical ensemble Monte Carlo calculations. [Preview Abstract] |
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H2.00040: A Novel Approach to Computational Protein Folding Molly Ball, Brittany Shannon, Christopher Fasano Protein function is controlled by the shape of the folded protein, so computing the shape of a folded protein is a critical part of understanding how proteins work and how they might be engineered to function in particular ways. We present preliminary results from a novel way of computing protein structure. We take the position that this problem should be treated quantum mechanically and we present applications of techniques from low energy nuclear physics (VMC and GFMC) to this problem. We discuss potential strengths and weaknesses of this approach given our early experiences in computing simple structures [Preview Abstract] |
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H2.00041: Stellar Coronal Physics with VLBI Imaging William Peterson, Robert Mutel We present the results of synoptic high-resolution imaging studies of two active binary star systems. Both were conducted using the VLBA-HSA at 15 GHz, making them the first images of extrasolar stars capable of discerning structure at scales smaller than a stellar diameter. Images revealed a giant coronal loop on Algol, filled with gyrosynchrotron flux at high activity levels and emitting from only the feet of the loop during quiescent epochs. UX Ari displays similar activity levels to Algol, but the components do not fill their Roche Lobes, making it an optimal comparison case for the role of mass transfer in the formation of global magnetic fields. [Preview Abstract] |
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H2.00042: Mechanical Deformation of Single- and Few- Layer Graphene on Micro-Scale-Grooved PDMS David Rocklin, Scott Scharfenberg, Cesar Chialvo, Richard Weaver, Paul Goldbart, Nadya Mason The physical properties of the material graphene are currently of wide interest. To explore their mechanical aspects, we placed graphene flakes, of thicknesses ranging from one to seven layers, on a rubbery PDMS (polydimethylsiloxane) substrate containing microgrooves. We used Atomic Force Microscopy (AFM) imaging techniques to study the resulting deformations of the surface, and found that the graphene adhered to the sample and substantially flattened the profile of the grooves. We have examined this flattening effect within a model based on linear elasticity theory. Thus, we have been able to identify, at least tentatively, the point at which shear stress breaks the interlayer coupling and causes the graphene layers to slide against each other. [Preview Abstract] |
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