Bulletin of the American Physical Society
2015 Annual Meeting of the APS Mid-Atlantic Section
Volume 60, Number 14
Friday–Sunday, October 23–25, 2015; Morgantown, West Virginia
Session BB1: Poster Session (5:00 pm-7:00 pm) |
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Room: MEC Lobby |
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BB1.00001: Examining the Time Variation of Electrostatic Fields of Pyroelectric Crystals Using A Scanning Electron Microscope Zumrad Kabilova, Benjamin Saeks Pyroelectric crystals are known for their instantaneous polarization under temperature change. In vacuum, the electrostatic fields due to their polarization are significant and useful for particle acceleration. We are using SEM (Scanning Electron Microscope) to evaluate the electrostatic fields of LiNbO3 crystals. In addition to scanning and producing magnified images, SEM's high voltage beam of electrons can serve as another measuring tool. In our project, we used the deflection of the beam under the influence of the electric field to measure the time-variation of field strength. These results were compared to experimental measurements of the crystal's surface charge to confirm that time-variation of the field strength behaved accordingly with the polarization and neutralization of charge. Furthermore, a theoretical model of the field production was developed to fit the experimental data. The path of the beam and the distribution of the electric field due to the crystal's surface charge were also modeled numerically using OOPIC simulation. The strength of the electrostatic fields were found to be in the range of 10 MV/m and were present for several minutes due to pyroelectric effect and slow neutralization of charge. [Preview Abstract] |
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BB1.00002: Cold neutron detection with far ultraviolet radiation from noble-gas excimers Michael A. Coplan, Timothy Koeth, Alexander L. Kowler, Mohamad I. Al-Sheikhly, Christopher M. Lavelle, Eric Miller, Alan K. Thompson, Robert E. Vest, Charles W. Clark The energetic MeV particles resulting from the capture of cold neutrons by $^{10}$B are used for the efficient formation of excimers in a surrounding noble gas at atmospheric pressure. Decay of the excimers results in the emission of far ultraviolet (FUV) radiation. Our measurements indicate that tens of thousands of FUV photons are produced for each neutron absorbed.\footnote{J. C. McComb, {\em et al., J. Appl. Phys.} {\bf 115}, 144504 (2014)} The detection of the photons forms the basis of an efficient, stable, and robust neutron detector. To increase efficiency, $^{10}$B films have been deposited on arrays of silicon substrates and B$_4$C coatings have been applied to reticulated vitreous carbon foams.\footnote{C. M. Lavelle, {\em et al., Appl. Phys. Lett.} {\bf 106}, 094103 (2015)} We have also begun experiments with wavelength-shifting compounds that convert the FUV radiation into visible light, which is then detected by a micro-photomultiplier. A detector research platform has been established on a dedicated cold-neutron beamline at the NIST Center for Neutron Research. Details of our recent work can be found at the Neutron Observatory website, http://j.mp/N3utr0n . [Preview Abstract] |
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BB1.00003: High-Mass Star Formation in the Outer Scutum-Centaurus Arm William Armentrout, Loren Anderson, Dana Balser, Tom Bania, Tom Dame, Trey Wenger Galactic HII regions are areas of ionized Hydrogen surrounding young, high-mass stars and can be detected across the entire Milky Way. The HII Region Discovery Survey (HRDS; Anderson et al. 2011; Bania et al., 2012; Anderson et al., submitted) has discovered nearly 1000 HII regions by detection of their Hydrogen radio recombination lines (RRLs) with the Green Bank Telescope. Using RRLs, we measure source velocity and determine position within the Galaxy by assuming a rotation curve, but until recently our sample in the far outer Galaxy was incomplete. A new spiral arm segment in the outer Galaxy was discovered by Dame {\&} Thaddeus (2011) and deemed the Outer Scutum-Centaurus arm, or OSC. This arm offers a new laboratory for the study of Galactic structure, high-mass star formation, and chemistry of the outer Galaxy. We searched for new Galactic HII regions in the OSC by targeting regions with an (l,b) location consistent with this arm and discovered 10 OSC HII regions thus far. Detected regions lie at an average distance from the Sun of 20.0 kpc and average distance from the Galactic center of 14.5 kpc with maximum solar distance of 23.5 kpc and maximum Galactic center distance of 17.0 kpc. These are the most distant known Galactic high-mass star formation regions. [Preview Abstract] |
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BB1.00004: Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe Hoyoung Kang, Massimo Ricotti We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies. [Preview Abstract] |
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BB1.00005: HII Region Ionization of the Warm Interstellar Medium: A Case Study of NGC 7538 Matteo Luisi, L. D. Anderson, Dana S. Balser, T. M. Bania, Trey V. Wenger The warm interstellar medium (WIM) is a low-density diffuse ionized component of the interstellar medium. Its ionization is likely maintained by photons from O-type stars, which are surrounded by spheres of fully ionized hydrogen, their HII regions. In order to ionize the WIM, these photons must escape through the photo-dissociation region (PDR), the boundary between the HII region within and the neutral medium surrounding it. Using data from the Green Bank Telescope, we analyze the ionizing radiation that is escaping through the PDR boundary of the HII region NGC~7538. We define the location of the PDR boundary, finding extended radio continuum and radio recombination line emission outside the PDR toward the north and east of the region. This suggests a non-uniform PDR morphology that is affecting the amount of radiation “leaking´´ through the PDR. We quantify the leaking photon fraction along the line of sight, and use a numerical model to estimate the leaking photon fraction in three dimensions of both radio continuum and H-alpha (656\,nm) emission. We detect carbon emission near the PDR and find a decrease in the helium-to-hydrogen ionic abundance ratio with increasing distance from the central position. This indicates a softening of the radiation field within the PDR. [Preview Abstract] |
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BB1.00006: Solar Flares and Magnetic Reconnection: Observations and Theory of the Elongation of Two-Ribbon Flares Milton Arencibia, Paul Cassak, Jiong Qiu, Dana Longscope Solar flares release enormous amounts of energy, up to ${10^{25}}$ J over timescales ranging from hours to a few seconds. Magnetic reconnection - the process through which magnetic fields in plasmas break and reconnect releasing energy - governs these events. One class of flares, two-ribbon flares, is characterized by the appearance in pairs of bright ribbons on the surface of the Sun that separate, interpreted as regions where material confined to reconnected magnetic field lines precipitate onto the solar surface and emit x-rays. Observations have revealed that ribbons, in addition to moving apart from each other, also elongate, thought to be related to the spreading of the reconnection site. 3D numerical simulations of magnetic reconnection have revealed that localized reconnection spreads in the direction normal to the reconnection plane either unidirectionally or bidirectionally depending on the strength of a “guide” magnetic field along the same direction. Observations also reveal that ribbons elongate either unidirectionally or bidirectionally with a similar dependence on the guide field, confirming the connection with the numerical results. We will further investigate the physics of two-ribbon flare spreading via a numerical parametric study. [Preview Abstract] |
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BB1.00007: Using BayesWave to Approximate Eccentric Black-Hole Binary Gravitational Waves Belinda D. Cheeseboro, Sean T. McWilliams The mission of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is to detect gravitational waves that could be caused by the interaction of massive gravitating bodies such as coalescing black holes and neutron stars. BayesWave is an algorithm that can analyze possible gravitational wave event data and determine the likelihood that the event strain contains mostly Gaussian noise, signal, or glitches. The algorithm accomplishes this by using multi-component models and incorporating the Reverse Jump Markov chain Monte Carlo (RJMcMC) to simultaneously perform model selection and fully sample the posterior likelihood to estimate model parameters. We will describe previous investigations using BayesWave, and discuss future work using BayesWave in a new way to detect gravitational wave signals from eccentric black-hole binary sources. [Preview Abstract] |
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BB1.00008: HI mapping capabilities using the Arecibo Observatory telescope Amy Sardone, D.J. Pisano Current HI mapping using the Arecibo Observatory telescope, the world’s largest single-dish radio telescope, has not produced images at its full capability, producing images with lower sensitivity and resolution. In order to search for possible signatures of gas accretion or debris from past gravitational interactions, we are attempting to produce images with the Arecibo Observatory telescope at it’s full capability, with the best resolution available for studies of faint, diffuse emission.Using data taken with the Arecibo Observatory telescope mapping HI in NGC 925, we were able to remove some of the artifacts from the initial reduction. These artifacts are a result of the non-Gaussian nature of the beam shape, produced by the unique optics of Arecibo. We are continuing to optimize the deconvolution of the beams. If we compare the HI mapping of the same galaxy using the Green Bank Telescope, we will be able to quantify the differences.With this method, we will be able to produce images at unprecedented sensitivity and resolution. This work serves as a demonstration of how astronomers will map HI using the Five hundred meter Aperture Spherical Telescope (FAST), being built in China. [Preview Abstract] |
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BB1.00009: Physical Models for Three Period-Changing Eclipsing Binary Stars Cameron Westerlund, Jason Ray, Matthew Beaky Eclipsing binary stars are star pairs that orbit around the system’s center of mass, with the plane of the orbit oriented such that the stars periodically block the other’s light as seen from Earth. If one star in the system evolves faster than the other, it may overfill its Roche lobe as it expands and transfer matter to the other star, which can be observed as a steady change in the system’s orbital period. Three overcontact eclipsing binary star systems that are known to have a changing orbital period, and which are suspected of experiencing mass transfer, were observed during summer 2015 at the Juniata College Observatory in Huntingdon, PA. Differential photometry was performed using Juniata’s 16-inch Schmidt-Cassegrain telescope and the 31-inch reflecting telescope at Lowell Observatory in Flagstaff, AZ. Using the modeling software PHOEBE, we analyzed the observed light curves to determine physical parameters of the neglected eclipsing binary star systems EG Canum Venaticorum, KN Vulpeculae, and V579 Lyrae. Complete light curves and preliminary models for these star systems will be presented. [Preview Abstract] |
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BB1.00010: Improving Radio Astronomy Surveys with a Low Noise Differential Amplifier Brittany Johnstone, Kevin Bandura We present here a differential low noise amplifier (LNA) to be used as an active balun on antennas for radio astronomy surveys. The LNA was designed around an Avago Technologies chip to be wideband while maintaining a low noise figure and unconditional stability. Design optimization was accomplished using Advanced Design System (ADS) to simulate component possibilities and layouts. After fabrication, the S-parameters of the LNA were measured between 10 MHz and 1.5 GHz showing that it is unconditionally stable within its working frequency band (100 MHz - 1 GHz). At 100 MHz it has a gain of 22 dB which decreases linearly to a gain of 15 dB at 1 GHz. The noise figure ranges between 0.3 dB at 100 MHz and 0.6 dB at 1 GHz and has an average value of 0.4 dB. In the future, we will attach the LNA to an antenna to test the performance of the system. [Preview Abstract] |
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BB1.00011: Transformation optics devices based on tapered waveguides William Zimmerman, Christopher Jensen, David Lahneman, Todd Adams, Thomas Gresock, Kathryn Zander, Vera Smolyaninova, Igor Smolyaninova Transformation optics (TO) gives rise to numerous unusual optical devices, such as novel metamaterial lenses and invisibility cloaks. However, it is very difficult to create metamaterials with low-loss broadband performance, especially in the visible frequency range. In our TO devices we use metal/dielectric waveguides to emulate metamaterial properties [1]. Here we report the first experimental realization of TO Luneburg lens waveguides and other novel TO devices [2]. The individual Luneburg lenses in the fabricated waveguides are based on lithographically defined metal/dielectric waveguides. We have studied wavelength and polarization dependent performance of the waveguides. Adiabatic variations of the waveguide shape enable control of the effective refractive index experienced by the TM light propagating inside the waveguide. Our experimental designs appear to be broadband, which has been verified in the 480-633 nm range. These novel optical devices considerably extend our ability to control light on sub-micrometer scales. [1]. V.N. Smolyaninova, et al., Phys. Rev. B 87, 075406 (2013); [2]. V.N. Smolyaninova, et al., Photonics 2, 440 (2015). [Preview Abstract] |
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BB1.00012: Semiclassical quantization of atomic systems through their normal form: The hydrogen atom Charles Jaff\'{e}, Patricia Yanguas, Jes\'{u}s Palaci\'{a}n, T. Uzer Over a century after Bohr's the initial quantization of hydrogen, the semiclassical quantization of atomic systems still represents a challenge. In the present paper we re-examine the semiclassical quantization of hydrogen asking the question: \textit{How can hydrogen be quantized without making use of its separability?} The approach adopted was to explicitly a construct transformation from the physical variables to the action-angle variables. The initial difficulty encountered is the lack of an equilibrium point on the potential energy surface. To surmount this difficulty, it is noted that the circular periodic orbits are relative equilibria. In a rotating frame the relative equilibria become critical points in the phase flow. It is shown that the flow in the vicinity of the critical point is stable. The Lie-Deprit transformation is then used to transform the system into normal form, following which the semiclassical quantization is straightforward. [Preview Abstract] |
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BB1.00013: Rotationally inelastic collisions of He and Ar with NaK: Theory and Experiment T. J. Price, A. C. Towne, K. Richter, J. Jones, C. Faust, A. P. Hickman, J. Huennekens, D. Talbi, R. F. Malenda, A. J. Ross, P. Crozet, R. C. Forrey Rotationally inelastic collisions of NaK ($A\,^1\Sigma^+$) molecules with He and Ar have been studied experimentally at Lehigh and at Lyon, providing information about population and orientation transfer. Theoretical calculations are also underway. We calculated HeNaK and ArNaK potential surfaces, carried out quantum scattering calculations of population and orientation transfer, and compared the results with experiment. The theoretical results show a propensity for $\Delta J =$ even transitions for He and for Ar, in good agreement with the measured cross sections. The calculations also determine cross sections for $JM \rightarrow J'M'$ transitions at large quantum numbers ($J \leq 45$), and we have developed a semiclassical model to address this limit. Our analysis invokes the vector model and leads to a closed form expression for the $JM$ to $J'M'$ cross sections. The model, which is in good agreement with exact quantum calculations, predicts that the polar angle $\theta=\arccos[M/(J+\frac{1}{2})]$ is approximately conserved, in agreement with several previous calculations and qualitative arguments. For many collisions the distribution of final polar angles is approximately Lorentzian. [Preview Abstract] |
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BB1.00014: Large effective three-body interaction in a double-well optical lattice Saurabh Paul, Eite Tiesinga We study ultracold atoms in an optical lattice with two local minima per unit cell and show that the low energy states of a multi-band Bose-Hubbard (BH) Hamiltonian with only pair-wise interactions is equivalent to an effective single-band Hamiltonian with strong three-body interactions. We focus on a double-well lattice with a symmetric double well along the $x$ axis and single well structure along the perpendicular directions. Tunneling and two-body interaction energies are obtained from an exact band-structure calculation and numerically-constructed Wannier functions in order to construct a BH Hamiltonian spanning the lowest two bands. Our effective Hamiltonian is constructed from the ground state of the $N$-atom Hamiltonian for each unit cell obtained within the subspace spanned by the Wannier functions of two lowest bands. The model includes hopping between ground states of neighboring unit cells. We show that such an effective Hamiltonian has strong three-body interactions that can be easily tuned by changing the lattice parameters. Finally, relying on numerical mean-field simulations, we show that the effective Hamiltonian is an excellent approximation of the full BH Hamiltonian over a wide range of lattice parameters, both in the superfluid and Mott insulator regions. [Preview Abstract] |
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BB1.00015: Evaluation of the Biocompatibility of the Bioinert Zirconia Using Computational Simulation Yeon Tae Chung, Saegyul Rhee, Gun Ha Seo One of the essential requirements of the biocompatible implants is restoring lost tissues. The choice of medical and dental implant materials is also important. To enhance the osseo-integration, researchers have been developing metal oxides, such as titanium oxides, as medical and dental implant materials. The improvements in new materials make it possible to have durable fixtures made of ceramic, which is commonly known as zirconia, a more tissue friendly material. Before fabricating a customized zirconia implant in a factory, it is recommended to test the stability of the molecular compound in order to verify its practical use. This paper shows how the zirconia implants perform better than the titanium oxide by employing computational chemistry methods. The commercial programs such as Gamess and Chemcraft have been used in an effort to discover the optimal method and to compute the measurements of stability. For the molecular diagrams, bond strengths are indicated by either a solid line or dotted line - greater the number, the stronger the bond. Any number greater than 1 is known to be very strong. If oxygen is not attached to the rest of the compound, it probably means the compound does not exist with oxygen. [Preview Abstract] |
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BB1.00016: Metamaterial approach to superconducting critical temperature increase Christopher Jensen, Kathryn Zander, Bradley Yost, Thomas Gresock, William Zimmerman, Joseph Prestigiacomo, Heungsoo Kim, Michael Osofsky, Shanta Saha, Richard Greene, Igor Smolyaninov, Vera Smolyaninova A dielectric response function plays a significant role in electron-electron interaction. Recently we proposed that the metamaterial approach to dielectric response engineering may increase the superconducting critical temperature. A composite superconductor-dielectric metamaterial has been tested in experiments with compressed mixtures of tin and barium titanate nanoparticles of varying composition. An increase of the critical temperature of the order of 5 percent compared to bulk tin has been observed [1]. Measurements of dielectric function was found to be in agreement with our model. A role of dielectric and particle size will be demonstrated. Different metamaterial approaches will be discussed [2]. [1]. V. N. Smolyaninova, et al., Scientific Reports 4, 7321 (2014); [2]. I. Smolyaninov and V. N. Smolyaninova, Phys. Rev. B 91, 094501 (2015) [Preview Abstract] |
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BB1.00017: \textbf{Magnetic Determination of the Electronic State of Cu and Exchange Interactions in the }$\alpha $\textbf{- and }$\beta $\textbf{-Phases of Molecular Semiconductor Copper Phthalocyanine (C}$_{\mathbf{16}}$\textbf{H}$_{\mathbf{32}}$\textbf{CuN}$_{\mathbf{8}}$\textbf{)} Zhengjun Wang, Kelly L. Pisane, Mohindar S. Seehra Among the transition metal phthalocyanines (TMPc, TM $=$ Mn, Fe, Co, Ni, and Cu) in which the TM atoms form linear chains along the b-axis, the electronic structure of CuPc has become of particular recent interest for applications in spintronics [1]. Here, using analysis of magnetization data in the $\alpha $- and $\beta $-phase of powder CuPc samples, the electronic state of Cu and exchange constant are reported. After verifying the crystal structure using x-ray diffraction, the temperature dependence (2 K to 250 K) of the magnetization M of both samples was measured in magnetic field H $=$ 1 kOe and isothermally at 2 K and 5 K in H up to 90 kOe. The data were analyzed first using the modified Curie-Weiss law, $\chi \quad = \quad \chi_{o}$ $+$ C / (T$+\theta )$, showing good fit for T \textgreater 4 K and yielding $\theta \quad =$ 2.3 K (0.2 K) for $\alpha $-CuPc ($\beta $-CuPc) and spin S $=$ 1/2 characteristic of Cu$^{2+}$. The data were next fitted to the Bonner-Fisher model for S $=$1/2 antiferromagnetic Heisenberg chain showing excellent fit to all the M vs. T data and yielding the Cu$^{2+}$-Cu$^{2+}$ exchange constant J/k$_{B}=$3.4 K ( 0.4 K) the for $\alpha $-CuPc ($\beta $-CuPc). The isothermal data of M vs. H is analyzed taking exchange into account. The large difference in the magnitudes of J/k$_{B}$ for the two phases is discussed in terms of the differences in their crystal structures [2]. [1] M. Warner et al, Nature, 503, 504-508 (2013). [2] Z. Wang et al, IEEE. Trans. Magn. ( in press, Nov. 2015 issue). [Preview Abstract] |
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BB1.00018: Band Gap Narrowing in Nitrogen-Doped La$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ with Transient Absorption Spectroscopy for Hydrogen Generation Brandon Yost, Scott Cushing, Nianqiang Wu, Alan Bristow Nitrogen doping was found to extend lanthanum dititanate's (LTO), La$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$, absorption from 380 nm to 550 nm giving a promising 2.3 eV bandgap for solar water splitting. The increased band gap in conjunction with a lack of mid-gap trap states allows for visible light photoactivity. In this presentation, transient absorption spectroscopy with both a supercontinuum and a THz probe confirm N-doping creates a continuum of states slightly above the valence band (VB) of intrinsic LTO without harming carrier lifetimes. Lifetimes are measured for carriers excited from the VB to the CB as well as from the dopant continuum to the CB. The measured lifetimes reveal lifetimes that are comparable to intrinsic LTO due to the minimal density of mid-gap states introduced by the nitrogen dopant. The THz probe confirms the visible light excited carriers are mobile and not trapped by measuring frequency dependent conductivity. Further, by adding reduced graphene oxide (RGO) and gold nanoparticles to the N-doped LTO, carrier extraction is further increased, tripling hydrogen generation. [Preview Abstract] |
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BB1.00019: COHERENT EXCITON-POLARITON MODEL FOR PHOTOSYNTHETIC ENERGY TRANSFER Richard Squire, Norman March, James Ingles If a bacterial photosynthetic light-harvesting complex absorbs a photon, the energy transfer to a charge separation complex some distance away is nearly perfect. This process has been described as coherent excitons, but we suggest that the mass is too high for this to occur at room temperature. Alternatively, we have presented a new photosynthetic model based on the existence of a reduce mass by combining photosynthetic excitons with photons to form a condensate called a polariton [1, 2]. Lidzey et al have recently reported strong polariton coupling between isolated photosynthetic chlorosomes and confined optical photons in a microcavity [3]. Here we discuss an expanded model which provides explanations for experimental measured extended coherence lifetimes and suggest that polaritons may have been already experimentally observed in native bacteria. \\ \\ $[1]$ J. J. Hopfield (1958) Phys. Rev. \textbf{112}, 1555. \\ $[2]$ R. H. Squire, N. H. March, R. Minnick$^{\dag }$, R. Turschmann$^{\dag }$ (2013) Int. J. Quantum Chem, \textbf{113}, 2181. \\ $[3]$ D. M. Coles, Y Yang, Y. Wang, R.T. Grant, R. A. Taylor, S. K. Sailkin, A. Aspuru-Guzik, D. G. Lidzey, J. K. Tang, J. M. Smith Nat. Commun. (2014) \textbf{5}, 5561. [Preview Abstract] |
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BB1.00020: Probing the uniaxial strains in MoS$_2$ using polarized Raman spectroscopy: A first-principles study Danna Doratotaj, Jia-An Yan Characterization of strain in two-dimensional (2D) crystals is important for understanding their properties and performance. Using first-principles calculations, we study effects of uniaxial strain on the Raman-active modes in monolayer MoS$_2$. We show that the in-plane $E'$ mode at 384 cm$^{-1}$ can serve as a fingerprint for the uniaxial strain in this 2D material. Specifically, under a uniaxial strain, the doubly degenerate $E'$ mode splits into two non-degenerate modes: one is $E_{\parallel}'$ mode in which atoms vibrate in parallel to the strain direction, and the other is $E_\perp'$ mode in which atoms vibrate perpendicular to the strain direction. The frequency of the $E_{\parallel}'$ mode blue-shifts for a compressive strain, but red-shifts for a tensile strain. In addition, due to the strain-induced anisotropy in the MoS$_2$ lattice, the polarized Raman spectra of the $E_{\parallel}'$ and $E_{\perp}'$ modes exhibit distinct angular dependence, allowing for a precise determination of the direction of the uniaxial strain. Thus, the polarized Raman spectroscopy offers an efficient non-destructive way to characterize the uniaxial strains in monolayer MoS$_2$. [Preview Abstract] |
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BB1.00021: \textbf{Energetic Resolution of State Filling by Surface Photovoltage Spectroscopy in Solar Energy Materials} Conner Castle, Brandon Yost, Scott Cushing, Nianqiang Wu, Alan Bristow Single semiconductors rarely possess the balance of spectral coverage and carrier lifetimes necessary for efficient photovoltaics or photocatalysis. This imbalance is commonly overcome by doping or heterostructuring, but subsequent introduction of defect and interface states weaken performance while being difficult to detect. Herein, we show that the surface potential formed by the differing charge diffusion rates of excited electrons and holes can be detected by surface photovoltage spectroscopy (SPV). SPV allows the excitation-energy dependent filling and lifetime of interface states, defect states, and band gap transitions to be separated, and is applied to characterize the improvement in electron and hole diffusion in a CdS@Au@TiO2 heterostructures while identifying losses from interface and defect states. The results show that Au can increase carrier transport between the two semiconductors while passivating surface states, improving the overall solar energy conversion efficiency. [Preview Abstract] |
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BB1.00022: Effects on the density of states of titanium dioxide by doping with sulfur Arturo Hernandez Zeledon, James Lewis $TiO_{2}$ is an attractive material for photocatalytic and photovoltaic applications, even though its maximum absorption happens around 4 eV, and the sunlight irradiance peak is between 1.5eV and 3.1eV. In this work we look for the effects of doping $TiO_{2}$ with sulfur, as one way to reduce the gap between the conduction and the valence states. We took the $TiO_{2}$ rutile structure as basis for random substitutions, in which we randomly select some oxygen atoms and we replace them with sulfur, making $TiO_{2(1-x)}S_{2x}$ for x = 0.1 and x = 0.25, then we relax the doped structures in order to find the stable configurations, then we select the lower energy structures to carry out the calculation of the density of states as a function of sulfur concentration. All the process and calculations are made using the FIREBALL software. [Preview Abstract] |
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BB1.00023: \textbf{Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO}$_{\mathrm{\mathbf{2.5+\delta }}}$ J. P. Carlo, M. E. Evans, J. A. Anczarski, J. Ock, K. Boyd, J. R. Pollichemi, I. A. Leahy, W. Vogel, A. J. Viescas A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABO$_{\mathrm{x}}$ have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO$_{\mathrm{6}}$ octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO$_{\mathrm{2.5+\delta }}$ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has $\delta =$0.5, this requires Fe$^{\mathrm{4+}}$, and hence strongly oxidizing environments. When grown in air, Fe$^{\mathrm{3+}}$ is favored, yielding $\delta \approx $0. SrFeO$_{\mathrm{2.5+\delta }}$ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO$_{\mathrm{2.5+\delta }}$ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. [Preview Abstract] |
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BB1.00024: Electrical and Structural Properties of Lattice-Mismatched Calcium Manganese Oxide Thin Films Cacie Hart, Zoey Warecki, Adeel Chaudhry, Natalie Ferrone, Grace Yong Electron-doped CaMnO$_{3-\delta}$ thin films are of interest for use in renewable energy applications because of their oxygen stoichiometry. We have investigated the properties of CaMnO$_{3-\delta}$ films epitaxially grown by pulsed laser deposition on LaAlO$_{3}$ and SrTiO$_{3}$ substrates,both of which have larger in-plane lattice parameters than CaMnO$_{3-\delta}$. This lattice-mismatch leads to bi-axial tensile strain in the thin films. We have characterized the thickness dependence of structural and electrical properties of these films using high resolution x-ray diffraction and temperature-dependent electrical resistivity measurements. We found that the thickness dependence is characteristically different from what has been preciously observed for hole-doped manganite thin films. Our results suggest that the electrical and structural properties of CaMnO$_{3-\delta}$ are related to a coupling between the tensile strain and the oxygen deficiency in the thin films. [Preview Abstract] |
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BB1.00025: The effects of alloying $CuAlO_{2}, CuGaO_{2},$ and $CuInO_{2}$ with $Fe$ at low percentage levels Ramon Beesley, Gihan Panapitiya, James Lewis Delafossite oxides are a family of materials with the form $ABO_{2}$, where the A-site is a monovalent cation ($Cu, Ag, Au$) and the B-site is a trivalent cation ($Ga, Al, In$). Within this family of material both p-type and n-type characteristics can be found. Delafossites typically have a wide optical band gap, this band gap may be tuned by adding a second B-site element forming an $AB^{1}_{(1-x)}B^{2}_{(x)}O_{2}$ alloy. The addition of the second B-site atom changes the electronic structure and may also enhance optical absorption. We studied the effects of alloying $CuAlO_{2}, CuGaO_{2},$ and $CuInO_{2}$ with Fe at 0\%, 1\%, and 2\% alloying levels. Using the FIREBALL program we optimized the atomic structure, calculated the total and partial density of states, calculated the valence band edge for each alloy level, and investigated the clustering factor of the second B-site atom in the 2\% alloys. From the partial density of state, we looked at each type of atoms contribution to the change in the valence band edge and found that $Fe$ is the major contributor to the change. [Preview Abstract] |
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BB1.00026: Pseudo-gap to band gap transition in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) observed by optical reflectivity/absorption Guerau Cabrera, Robbyn Trappen, Mikel Holcomb, Y-H Chu Thin film La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) is a prime candidate for highly spin-polarized magnetic-tunnel-junction memories. Due to its magnetic properties, it is also a good candidate for applications utilizing electrical control of magnetism when grown adjacent to a ferroelectric layer such as Pb(Ti/Zr)O$_{3}$ (PZT). Recently, Wu and others have seen the emergence of a band gap (~1eV) in LSMO thin films, when grown adjacent to PZT. Currently, it is understood that LSMO is a half-metal, with a pseudo-gap due to a low desity of states (DOS) near the Fermi level. The transition from pseudo-gap to band gap is not yet fully understood. It is therefore our aim to investigate the emergence of this band gap through optical reflectivity/absorption and thickness dependence experiments. [Preview Abstract] |
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BB1.00027: Simulation of Photo-isomerization of Functionalized Azobenzene Derivatives Pedram Tavazohi, Zachary Herberger, James Lewis Photo-isomerization is the process of changing the isomer ($cis$ or $trans$) of a molecule using light. In azobenzene this process can be utilized in a Metal Organic Framework (MOF) for adsorption of CO$_{2}$. MOFs are created by two major components, metal ions, and organic molecules which are usually called linkers. The metal ions and linkers can be coordinated in a way that they form a porous material. In the $cis$ isomer of azobenzene, the MOF’s pore is available to be filled by CO$_{2}$, but in the $trans$ isomer the pore is filled with a benzene ring. The change from $cis$ to $trans$ will evacuate the pore if CO$_{2}$ is present. The important considerations in using azobenzene photo-isomerization as a photo-switch in MOFs are, the quantum yield of the process, and the wavelength of the light which triggers photo-isomerization. By substitution of the functional groups of azobenzene and using the FSSH algorithm in FIREBALL to simulate the photo-isomerization process we can tune the properties of the molecule as we desire and predict the best substitution sites for azobenzene functional groups. We studied the effects of functionalizing the molecule with OH, CH$_{3}$, NH$_{2}$, and COOH on isomerization quantum yield. [Preview Abstract] |
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BB1.00028: Ti-Ni Crystal Structure Prediction by Minima Hopping Method Adam Payne, Irais Valencia-Jaime, Guillermo Avendaño-Franco, Raymundo Arroyave, Aldo Romero Titanium alloys have wide applications from industry to medicine due to their unique properties of shape memory and superelasticity. While it is known that these amazing properties result from an interplay between titanium’s low temperature cubic $\beta$ phase and its high temperature hexagonal phase, the exact nature of this interplay is poorly understood. Investigating how the elastic properties vary with composition is crucial to understanding this mechanism. We have performed a structural search method known as Minima Hopping [1] to identify the ground state structure in thirty-one compositions. We also identify metastable structures, which are of interest because they can be stabilized with the addition of other atoms. We found the convex hull, and have compared it to known experimental and computational results. Elastic, electronic, and energetic properties are computed for the ground state structures using first-principle calculations as implemented in the VASP code. [2] We report the structures with interesting elastic and vibrational properties, and convey several options for future work. [1] Buehler, W. J., R. C. Wiley. No. NOLTR- 61-75. Naval Ordnance Lab White Oak MD, 1961 [2]S. Goedecker, The J of chem phys 120,9911 (2004) [Preview Abstract] |
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BB1.00029: ZnO Thin-Film Transistors as a Transduction Platform for an Electronic Nose Michael Aldridge, Prakash Gajurel, Fabiola Al-Ibrahim, Everett Daly, David Lederman, Letha Sooter, Cerasela-Zoica Dinu, Kevin Daly Technology has emulated, and in many cases improved upon, most of the human senses. However, the chemical senses have historically been overlooked. Molecular recognition elements (MREs) such as aptamers have been available for years, but a key challenge in chemical sensing is the transduction of this molecular binding event into a measurable signal. Here, we demonstrate the use of a ZnO thin film field effect transistor (TFFT) as a suitable platform for transduction. ZnO TFFTs were fabricated with a back-gate configuration on Si/SiO2 substrates using RF magnetron sputtering. TFFTs were bio-functionalized with DNA aptamers using ethoxysilane- based conjugation chemistry. The transfer properties of the TFFTs were used as a proxy for the change in surface properties caused by the aptamer binding event. The functionalized TFFTs showed a decrease in current after exposure to the target analyte (adenosine triphosphate, ATP). Subsequent exposures to increasing concentrations of ATP were accompanied by further decreases in current. Based on the preliminary results, these TFFTs provide a sensitive and durable platform for reporting molecular binding events. [Preview Abstract] |
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BB1.00030: A Study of the Dielectric Materials and Metal Organic Framework Nano Particles in Electrochemistry Hojung Chun, Bokeun Kwon, James Kwon In recent years, the development of nano technology has been arising in many technological fields, such as electro chemical fields.~When the space between the plates of a capacitor is filled with an insulator, the capacitance of the capacitor is predicted to improve. In this research, the influence of multiple dielectric materials inserted in one capacitor on the electric field distribution in the capacitor system was studied. Patterns of the capacitances were found, and the electric charges and electric energy in the capacitor plates were calculated. A supercapacitor can hold hundreds of times more electrical~density~than a standard capacitor.~In this study, we show how metal-organic frameworks (MOFs) can be integrated into supercapacitor devices, and how the flexibility with which their metal oxide and organic constituents can be varied and used to uncover their high capacitance and long lifecycle behavior. This study examines how metal-organic frameworks (MOFs) made as nanocrystals (nMOFs) can be successfully incorporated into electrical devices to be used as supercapacitors. Using this mechanism, a MOF with multiple metal ions and organic functionalities is suggested. [Preview Abstract] |
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BB1.00031: Two quantum coherent spectroscopy of excitons in strained bulk GaAs Brian Wilmer, Daniel Webber, Kimberley Hall, Alan Bristow Two-dimensional Fourier transform spectroscopy is used to measure the third order optical response from excitons in bulk GaAs. The degeneracy of the heavy and light hole excitons is lifted due to biaxial strain. This allows for the observation of coherent coupling features between the heavy and light hole resonances in spectra. This system differs from quantum wells, due to the lack in inhomogeneity, and is a model system for isolating many-body interactions without quantum confinement. Within the system, electrons and holes, requiring only one unit of excitation, can bind to form one quantum (1Q), excitonic states. With a second unit of excitation, the two quantum (2Q) excitation manifold can be accessed. While 1Q, rephasing spectra indeed have 2Q contributions, the peaks are crowded in single plot and difficult to resolve. 2Q scans have no 1Q contributions and allow for clear isolation of all coherences of that manifold. The sample exhibits states from bound heavy, light, and mixed (heavy and light)-hole biexcitons, as well as unbound yet correlated excitons, electron hole pairs, and scattering states. Polarization allows selection of certain states. [Preview Abstract] |
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BB1.00032: Big Bang or Big Bounce? Paul Steinhardt Did the universe begin with a bang fourteen billion years ago, as conventionally assumed? Or was there a bounce --- a transition from a period of contraction to expansion? This talk will briefly recount the historical views of Einstein and his contemporaries a century ago and then focus on how these questions have become the key to interpreting recent and forthcoming observations and to our understanding of the origin and future of the universe. [Preview Abstract] |
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BB1.00033: A Novel Approach for Rapidly Generating Supermassive Black-Hole Binary Populations Using the Schechter Function Trey McNeely, Sean McWilliams Some simulations of the stochastic background of gravitational radiation due to supermassive black-hole binaries rely on a simple power law distribution in the chirp mass, a particular combination of the masses that determines the signal strength, to generate the population. The more physical Schechter function provides a more accurate population for individual black-hole masses, but using it to generate a chirp mass distribution poses several computational problems, including its large dynamic range and time complexity of generating a population from a distribution in the individual masses rather than the chirp mass directly. These problems can be overcome by numerically inverting the definition of chirp mass and generating a univariate chirp mass distribution from the bivariate Schechter function of the individual masses. This is a nontrivial task, but accomplishing it, as we will show, allows us to generate models for the full gravitational-wave signal much more efficiently. [Preview Abstract] |
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BB1.00034: Rh-based Catalysts for the Ethanol Conversion as an Alternative Fuel Additive Jaewon You, Jeremiah Yoon, Chung Un Lee Oil is definitely the most important of all the energy sources and fossil fuels have accounted for the most of the energy produced. Ethanol is not an efficient~fuel, but it~is well-known to act as~a great fuel additive.~To improve fuel~efficiency, researchers~have discovered~ways to~add~ethanol~to~gasoline combustion.~Catalytic oxidation reactions are crucial for chemical synthesis in pharmaceutical and petrochemicals industries. Rhodium(Rh) is a major component of industrial catalytic systems, and it is found as free metal, along with nickel and copper deposits. The focus of this project is the study of catalysts for the conversion of ethane to ethanol that can be used as a fuel additive: Rhodium dichlorine monoxide(RhCl$_{\mathrm{2}}$O), Rhodium oxide(RhO), and Rhodium hypochlorite(RhClO).~The catalytic efficiency of those compounds will be modeled and explained based on the compound's electron structure and how the catalytic efficiency could be improved even~more~by forcing the catalyst to react with ethane in different ways.~Computational chemistry~will be used to~find the~best catalyst for the conversion of ethanol, which will advocate the ethanol~economy. [Preview Abstract] |
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BB1.00035: Self-Efficacy and Belonging in Introductory STEM Majors. Rachel Henderson, Seth DeVore, John Stewart Students' sense of self-efficacy and belonging may be situated in many environments in a college setting. Two surveys that measure student's feelings of self-efficacy and belonging within their STEM and campus communities were administered to over 550 introductory level, calculus-based, physics students at West Virginia University (WVU) during the spring 2015 semester. An exploratory factor analysis was performed to determine the important elements of self-efficacy and belonging that are prevalent among incoming students in STEM fields. We will discuss the breakdown of these elements as they pertain to the physics sequence, classes within the student's major, perceptions of the student's future career, and between these elements will also be presented. This project provides further opportunities to explore the development of student feelings of self-efficacy and belonging and how they relate to STEM retention and performance. [Preview Abstract] |
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BB1.00036: Self-Regulation and Performance in Introductory Physics John Stewart This poster examines the degree to which students regulate their study activities and time-on-task in calculus-based introductory physics. Ten years of class performance data from a large Midwestern university is combined with self-reported time-on-task and study behavior data collected using a survey instrument. The degree to which student behavior evolves within the semester due to the stimuli of either low or high test grades is presented. The changes in student time use and behavior patterns are also investigated longitudinally as the course studied underwent revision. Students regulate their reported study time for exams as a result of varying exam grades but there is little evidence of regulation of the time investigates in other behaviors such as working homework. [Preview Abstract] |
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BB1.00037: Physics Experiments in the Electronics Lab Course Everett Ramer A total of 12 experiments representing mechanics, heat, sound, electricity, and light were added to the electronics lab course for physics majors between the instructional material on analog and digital electronics, and the student-initiated end-of-semester projects. The goals were to provide projects that reviewed and reinforced material studied throughout the semester, and to demonstrate that this material can be useful in the laboratory setting. The experiments were simple, each one was completed by a single student during a single three-hour lab session. They were specifically designed to use the same circuits and Arduino sketches the students had constructed during the instructional portion of the course. For example, a phototransistor circuit from the BJT analog lab was combined with an interval-timing Arduino sketch from one of the digital labs to measure the gravitational acceleration of a falling ``picket fence.'' Student response was very positive, often citing appreciation for the wide range of physics experiments that could be performed with only a handful of very simple circuits and Arduino sketches. [Preview Abstract] |
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BB1.00038: Examining the Effects of Testwiseness Using the FCI and CSEM Seth DeVore, John Stewart Testwiseness is generally defined as the set of cognitive strategies used by a student and intended to improve their score on a test regardless of the test's subject matter. To improve our understanding of the potential effect size of several elements of testwiseness we analyze student performance on questions present in the Force Concept Inventory (FCI) and Conceptual Survey on Electricity and Magnetism (CSEM) that contain distractors, the selection of which can be related to the use of testwiseness strategies. Additionally we examine the effects of the position of a distractor on its likelihood to be selected in 5-option multiple choice question. We further examine the effects of several potential positive and negative testwiseness effects on student scores by developing two modified versions of the FCI designed to include additional elements related to testwiseness. [Preview Abstract] |
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BB1.00039: Cost-effective containment of unmagnetized argon plasma using a magnetic bucket and a helicon source Miguel Henriquez, M. Umair Siddiqui, Earl Scime We demonstrate highly-ionized and unmagnetized plasma production in the~low-power Compact HElicon for Waves and Instabilities Experiment (CHEWIE) at~West Virginia University. To achieve this, the argon helicon plasma is injected into a multidipole-confined expansion chamber. Using Langmuir probes~and optical emission spectroscopy, we calculate ionization fractions in the~unmagnetized volume as a function of input power and fill pressures.~Finally, we investigate the ionization efficiency power scaling to determine~if helicons are cost-efficient plasma sources for larger highly-ionized,~unmagnetized plasma experiments. [Preview Abstract] |
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BB1.00040: Spatially Resolved LIF Measurements of a Current Free Double Layer in an Argon Helicon Plasma Evan Aguirre, Umair Siddiqui, Earl Scime We report preliminary 2-dimensional, spatially resolved observations of a double layer in an expanding helicon plasma. These new measurements investigate the origins of previously observed multiple ion beam populations in the downstream plasma. We use Laser Induced Fluorescence (LIF) to measure the ion velocity distribution functions (IVDFs) of argon ions and neutrals both parallel and perpendicular to the background magnetic field and an rf-compensated Langmuir probe to determine the local plasma potential. These are the first multi-dimensional LIF measurements of ion acceleration in a current-free double layer and were obtained with a recently installed, internal scanning probe system in the HELIX-LEIA experimental facility. [Preview Abstract] |
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BB1.00041: Ion flow characterization of the plasma boundary in a helicon plasma Derek Thompson, Umair Siddiqui, Julianne McIlvain, Zachary Short, Earl Scime Experimental investigation of plasma interface physics is critical for verifying plasma boundary models. In addition to strongly affecting discharge volume bulk properties, plasma boundary interactions are particularly important for fusion energy devices and for electric propulsion, where walls can be degraded via plasma bombardment. We present the results of two experiments. In the first experiment, the magnetic field is aligned parallel to an absorbing boundary and ion-neutral collisions are varied while measuring bulk ion flows with laser-induced fluorescence (LIF). The data are compared to drift models and indicate that collisional diffusion accounts for ion transport toward the boundary, except when low-frequency electrostatic fluctuations are present in the plasma. When fluctuations are observed, the classical model underestimates radially outward ion flow. In the second experiment, an absorbing boundary is placed at oblique incidence to the background magnetic field. Ion distributions near the boundary are measured with LIF to investigate how the electric fields, present at plasma interfaces, affect ion flows and transport near the boundary surface. These experiments represent the first radial and 3D measurements of ion flows in these scenarios. [Preview Abstract] |
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BB1.00042: Microwave Assisted Helicon Plasmas. John McKee, Umair Siddiqui, Miguel Henriquez, Zach Short, Earl Scime Up to 1.2 kW of pulsed 2.45 GHz microwaves are injected into argon and helium helicon plasmas at 6 to 20 mTorr neutral pressure, at 500 W of continuous rf power, and up to 1 kG magnetic field strengths. The objective is to heat the tail of the electron energy distribution function (EEDF) and populate ion metastable states for investigation with laser-induced-fluorescence. Langmuir probes are used to measure the EEDF and optical emission spectroscopy is used to monitor ion emission from excited states populated by the additional microwave power. The injection of microwave power in argon helicon plasmas is shown to heat the high energy tail of the EEDF without increasing the plasma density. Argon ion emission is shown to increase by a factor of 4. Injection of microwaves into a helium helicon plasma is shown to cool the bulk of the EEDF and increase the plasma density. Previously absent helium ion emission lines are observed with the injection of microwaves. [Preview Abstract] |
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BB1.00043: Three-dimensional laser-induced fluorescence measurements in a helicon plasma source Julianne McIlvain, M. Umair Siddiqui, Zachary Short, Miguel Henriquez, Earl Scime We describe an upgrade to our two-dimensional laser-induced fluorescence (LIF) diagnostic that enable measurements over a three dimensional volume of plasma. With this new capability, we have measured the flow of ions and neutrals in an argon plasma toward a stainless steel, grounded plate aligned perpendicular to the magnetic field in a helicon plasma source. We present measurements of the three-dimensional flow field in this three-dimensional volume as a function of the magnetic field strength and rf power in the helicon source. [Preview Abstract] |
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BB1.00044: Comparison of established and novel laser-induced fluorescence schemes for Ar I Zachary Short, M. Umair Siddiqui, Miguel Henriquez, John McKee, Julianne McIlvain, Earl Scime, Amy Keesee, Drew Elliott To explore ion-neutral coupling in plasmas, it is advantageous to be able to measure the velocity distribution function (VDF) of ions and neutrals simultaneously at a single spatial location. While in previous experiments we have successfully performed neutral and ion VDF measurements with a single laser, the Ar I laser induced fluorescence (LIF) scheme used was limited to operational regimes that were unsuitable for LIF measurements of Ar II. Here we describe a novel infrared LIF scheme for Ar I using a Sacher tunable diode laser and compare it to the previous Ar I LIF scheme [\textit{Keesee et al.} Rev. Sci. Instrum. \textbf{75}, 4091 (2004)]. In contrast to the previous method, our LIF scheme collects emission light that has no other natural argon emission lines nearby, decreasing the non-signal radiation collected by the detector, thus reducing the noise background. In addition, we present corrected iodine cell spectra for the previous Ar I LIF scheme. [Preview Abstract] |
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BB1.00045: Miniaturized Energy Spectrometer for Space Plasma Measurements Raphaela Goes de Lima, Earl Scime, Amy Keesee, Greg Lusk Taking advantage of technological developments in lithographic fabrication techniques over the past two decades, we have designed an ultra-compact plasma spectrometer that requires only low voltage power supplies, no microchannel plates, and has a high aperture area to instrument area ratio. The designed target is for ions in the 3- 20 keV range with a highly directional field of view. In addition to reducing mass, size, and voltage requirements, the new design will revolutionize the manufacturing process of plasma spectrometers, enabling large quantities of identical instruments to be manufactured at low individual unit cost. Such a plasma spectrometer is ideal for Heliophysics plasma investigations, particularly for small satellite and multi-spacecraft missions. Here we present initial measurements of the performance of the instrument components and designs of the electronics for the low energy threshold solid state detector. [Preview Abstract] |
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BB1.00046: Asymmetric magnetic reconnection with flow shear: PIC simulations and magnetopause applications Paul Cassak, Christopher Doss Magnetic reconnection at Earth’s dayside magnetopause typically has significant asymmetries in both magnetic field strength and plasma density. In addition, a flow shear across the reconnection site in the plane of the reconnecting magnetic field can be caused by magnetosheath flow, especially at higher latitudes. Predicting the solar wind’s effect on reconnection is important for understanding, e.g., solar wind-magnetospheric coupling. Recently, we showed that flow shear during asymmetric reconnection causes the reconnection site to convect in the outflow direction, predicted the flow speed from momentum conservation, and confirmed the results with two-dimensional two-fluid numerical simulations. We also predicted and confirmed with two-fluid simulations the reconnection rate as a function of upstream plasma conditions and the flow shear required to shut reconnection off. Here, we revisit this using two-dimensional particle-in-cell (PIC) simulations, which treat plasma mixing in the exhaust more realistically than the fluid model. We find good agreement between the predictions and PIC simulation results for both the X-line convection speed and the reconnection rate for flow speeds below the cutoff speed. Applications to the dayside magnetopause will be discussed. [Preview Abstract] |
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BB1.00047: \textbf{Dynamics of the magnetospheric field-aligned current distribution during magnetic storms} Dimitris Vassiliadis, Bruce Tepke Generation of field-aligned currents in a plasma is related to its dynamic stability and energy balance. Once developed, the currents may couple distant regions through particle transport and dissipation of electromagnetic stresses. Field-aligned currents at the magnetosphere-ionosphere interface provide coupling between the plasmas, and are linked to electron precipitation and the development of auroral structures. Closing the currents in the ionosphere are the auroral electrojets with space weather effects on power grids and pipelines. Thus, resolving questions on the location and duration of the currents can help identify how energy incident on the ionosphere is absorbed and transmitted. We use magnetometer data from a constellation of 66 Iridium satellites in the AMPERE project to measure the spatial distribution of the radial current density J$_{\mathrm{r}}$(MLT, MLAT) on a geomagnetic coordinate grid. In four recent storms we find good agreement between the peak amplitude of J$_{\mathrm{r}}$ and the auroral electrojet indices compiled from ground magnetometer data. Hemispheric conjugacy is observed in each event. Both types of magnetospheric activity are ultimately driven by the convection electric field in the solar wind, \textbf{E}$=$\textbf{v}x\textbf{B}. To model the solar wind driving we use a magnetohydrodynamic (MHD) model provided by NASA Goddard Space Flight Center's Community Coordinated Modeling Center. We find very good agreement between the observed and MHD time evolution of density J$_{\mathrm{r}}$ during the storms. [Preview Abstract] |
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