Bulletin of the American Physical Society
9th Annual Meeting of the Northwest Section of the APS
Volume 52, Number 6
Thursday–Saturday, May 17–19, 2007; Pocatello, Idaho
Session C1: Poster Session (4:00-6:00 p.m.) |
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Chair: E.M. Henley, University of Washington Room: IAC/PSI Idaho Accelerator Center/Positron Systems Inc. |
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C1.00001: Critical Single-Point Mutations and Protein Folding Pathways. Roy Campbell Single-point mutations can have a dramatic effect on protein structure. Treating a mutation as a perturbation of a protein's folded structure may not reveal a significant effect on that structure. The dependence of a protein's structure on a mutation may only be understood when the mutation's effect on the folding pathway is known. A united-residue model (Liwo \textit{et al}., PNAS, \textbf{102}, 2367, $2005)$ was used to study the effect of single-point mutations on protein folding pathways. [Preview Abstract] |
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C1.00002: Magnetoelectric Properties of Magnetic Tunneling Junctions Shilpa Chava, Avishesh Dhakal, Wei Jiang Yeh Magnetic tunneling junctions(MTJ's) consisting of two ferromagnetic layers separated by a thin insulating barrier show large tunnel magnetoresistive effects when the magnetizations of the ferromagnetic layers change their relative orientation from parallel to antiparallel in an applied field. Tunnel magneto resistance (TMR) is defined as the relative difference in tunnel resistance between parallel and antiparallel oriented magnetizations of electrodes. The larger this TMR effect, the more sensitive the MTJ will be as magnetic read out device. This result has attracted considerable attention due to its potential applicability in digital storage industry and as magnetic field sensors. In this study we present our experimental evidence of magnetoelectric properties of MTJ's. Co(30nm)/Al2O3(1.5nm)/NiFe(30nm) tunnel junctions were fabricated on a Si wafer using DC plasma sputtering deposition with shadow mask technique. We used the RF plasma in-situ oxidation method to oxidize the thin Al layer. We measured the magnetoresistance(MR) ratio of these junctions at room temperature by applying magnetic field in plane and perpendicular to the direction of current. We could obtain MR values of 8\% at room temperature and the resistances of these junctions were found to be 500O to 50 KO range. [Preview Abstract] |
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C1.00003: The Radioactive Decay of Beryllium-7 Kellen Giraud, Grant Hart, Bryan Peterson, Takeshi Nakata There are about 95 radioactive isotopes that decay exclusively through electron capture. The energy available for decay is not adequate for electron-positron pair production, the only other possible route for an atom that is neutron-poor to decay. Beryllium-7 is the lightest isotope that decays only through electron capture. Because Be-7 requires the presence of electrons to decay it is possible to modify the decay rate by modifying the electronic structure of the atom through chemical bonding, application of high pressure, or ionization. And because Be only has 4 electrons this effect is much stronger than in heavier elements. Be-7 is naturally found in two locations that are of interest to us: in the core of the sun as part of the fusion cycle, and in the atmosphere due to cosmic ray interactions with atmospheric gases. I will present an overview of where the Be-7 comes from, what happens to it after it is formed, and some areas, such as geology and stellar physics, where information about Be-7 can be used to understand other processes. I will then describe the efforts that are currently underway at BYU to trap a non-neutral plasma comprised of ionized Be-7 to investigate the effect of ionization on the decay rate. [Preview Abstract] |
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C1.00004: EPR and ENDOR of Nd$^{3+}$ in congruent and stoichiometric LiNbO$_{3}$ Valentin Grachev, Galina Malovichko, Mark Munro Since many years Lithium Niobate (LN) is of great interest for both fundamental science and applications because of the unusual richness of its ferro-, pyro- and piezoelectric properties. Conventional LN crystals, grown from a congruent melt with lithium deficiency, contain some percent of intrinsic defects. Samples grown under special conditions from melts, to which potassium has been added, have reduced contents of intrinsic defects and lower disorder (stoichiometric samples). Both congruent and stoichiometric crystals doped with neodymium were studied with the help of the electron paramagnetic resonance, EPR. Tremendous narrowing of the EPR lines in stoichiometric samples in comparison with congruent ones allowed us to distinguish four non-equivalent centers, as well as line splitting caused by hyperfine interaction of neodymium electrons with nuclear spins of magnetic isotopes $^{143}$Nd and $^{145}$Nd. One of the centers has axial C$_{3}$ symmetry, whereas others have lowest C$_{1}$ symmetry due to presence of intrinsic defects or/and charge compensation defects in the near neighborhood of Nd$^{3+}$. Narrow EPR lines allowed us also to investigate Electron Nuclear Double Resonance (ENDOR). Structures of the Nd$^{3+}$ centers derived from the EPR/ENDOR data and effects produced by micro- and macro-imperfections of LN crystals are discussed. [Preview Abstract] |
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C1.00005: Measurement of Radiation Induced Damages in Semiconductor Materials Useful as Photovoltaic and Nuclear Detection Devices Rubi Gul, Kara Keeter, Rene Rodriguez Radiation interactions with materials cause a change in electronic and physical properties of the material, which affect the performance of the devices. It is a key issue in the employment of these materials in medical, space, security and other scientific applications. In our research we have determined the defects and their generation rate induced by gamma rays of energy 0.11-22 MeV, in CuInS$_{2}$. We have used a simple model consisting of classical physics principles and Monte Carlo simulation software. The simulation results are in agreement with other published results done for other semiconductor materials. Our collaborators at INL will investigate different techniques for fabrication of thin films of CdZnTe and CuInS$_{2}$ by using Radiofrequency Pulsed Plasma Enhanced Chemical Vapor Deposition and Pressurized Solvent techniques. Next, defects will be induced in the thin-film samples by exposure to a bremsstrahlung gamma-ray beam. The radiation dose will range from 5 to 25 kGy. Qualitative and quantitative measurements of the defects in the crystals will be done by gamma-ray spectroscopy and PICTS (Photo induced current transient spectroscopy). [Preview Abstract] |
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C1.00006: Comparison of Several Approaches to the Nuclear Incompression Modulus David Hudson The nuclear incompressability modulus (K) is an important factor for determining the equation of state of nuclear matter. It is however, not a directly measurable quantity. In this presentation, I compare two complementary approaches for determining K. One is the excitation of Giant Monopole and Giant Dipole Resonances by alpha particle scattering. The other is by alpha decay. The role of various assumptions and input uncertainties in the analysis and their relation to the value of K will be discussed. [Preview Abstract] |
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C1.00007: Dark Matter Self Interaction Limits: Determination and Implications Paul Lessard The first studies of the lensing events around the Bullet cluster have shown that the dark matter halos of galaxy clusters are collisionless. This rather fortunate structure in the universe becomes an excellent laboratory for setting limits on the source of dark matter particle interaction. Markevitch et al. in 2004 explored three simple methods for determining the dark matter self interaction cross section to mass ratio.. A new strong and weak lensing derived density map of the cluster has been created, advancing the accuracy of these limits. A subsequent Markevitch et al. paper was released April of this year with a full n-body simulation of the collision putting giving us the best, although not the strongest, limit on the dark matter self interaction cross-section to mass ratio. Furthermore we are now at such a point as to ask what these limits tell us. Axions and SUSY wimps theoretically fall well under this threshold leaving their DM candidacy untouched if not strengthened. Other candidates like Q-balls however, are not guaranteed to fall below this limit. It is my goal to characterize Q-ball dark matter scenarios coincident with this new experimental limit. [Preview Abstract] |
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C1.00008: Beam Dynamics Studies in the RACE Project: MH1 transport line --low power regime operation- Carlos Maidana, Alan Hunt, Denis Beller As part of the Reactor Accelerator Coupling Experiments (RACE) a set of preliminary studies were conducted to design a transport beam line that could bring a 25MeV electron beam from a linear accelerator to a neutron-producing target inside a subcritical nuclear system. Because of the relatively low energy beam, the beam size and a relatively long beam line (implicating a possible divergence problem) the MH1 transport line was designed. Beam dynamics studies followed the beam optics ones and we present in this paper the first results of such studies. [Preview Abstract] |
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C1.00009: Analyzing Flare Ribbons to Determine Magnetic Reconnection Flux and its Relationship to Flux Rope Formation Jada Maxwell, Jiong Qiu, Richard Canfield Is the helical structure of a magnetic cloud (MC) largely pre-existing before its eruption or formed in situ by magnetic reconnection in the solar corona during the eruption? The flux of magnetic reconnection in the low solar corona can be evaluated through the flare ribbons observed in the chromosphere. Using data from TRACE and SOHO MDI, we measure the total magnetic reconnection flux swept up by flare ribbons in events associated with coronal mass ejections (CME). We compare this to MC flux measured in situ at 1 AU and find a near linear scaling pattern between MC poloidal flux and total reconnection flux. This relationship suggests that low corona reconnection is highly relevant to flux rope flux for the samples in our study. We note that this relationship does not distinguish events with or without filament eruption. Therefore, filaments may not play a role of carrying a significant amount of pre-existing flux. [Preview Abstract] |
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C1.00010: An Analysis of GRB 070110 Gabrielle Sloane The Gamma Ray Burst 070110 has an unusual X-ray afterglow light curve, with an extremely flat section between the initial and final decay periods with some flaring. The optical afterglow was also unusually long-lasting. It is a long burst (more than 2s), pointing to a collapsing very massive star as progenitor. However, the afterglow does not coincide with typical light curves (very steep, then shallow followed by increasing decay) seen in most long GRBs and corresponding to an immediate collapse by the progenitor into a black hole. Using available data, I analyze this burst source and propose various scenarios that might lead to the observed afterglow. [Preview Abstract] |
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C1.00011: Is increased Nuclear Energy a practical response to Global Warming? Jeanne Stevens With the threat of global warming there has been renewed interest in nuclear energy as a carbon-free energy source. There are currently 15 nuclear power plants planned for completion in the U.S. by 2014. In the last 30 years, however, investment and public support for nuclear energy has been minimal. Some factors that led to this loss of interest - high economic costs, risk of accident and radiation exposure, and the challenges of storing nuclear waste - have been analyzed in several recent publications. Comparing the costs and risks of nuclear energy to the benefits in reduced carbon emissions is the goal of this report. Coal plants contribute the most carbon dioxide of all types of power plants. The method of this study is a direct comparison of coal plants and nuclear plants in four areas: the current cost per kWh, the predicted annual cost for health issues, the statistically predicted deaths, and the clean-up costs assuming each facility is as ``green'' as possible. A normalized cost/risk value is then calculated for each plant type. Discussion for how these values are likely to vary is included. [Preview Abstract] |
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C1.00012: ABSTRACT WITHDRAWN |
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C1.00013: Development of a low cost 3D Particle Image Velocimetry for sub-sonic wind tunnel applications in Idaho State University. Carlos O. Maidana, Marco P. Schoen, Kalyan Jinnuri, Brian G. Williams, Lawrence Beaty PIV is a non-intrusive technique that provides instantaneous velocity vector measurements in a cross section of a flow. The stereo or 3D PIV technique is a topic of current interest due to its capability of 3D mapping of the vector field. We present in this paper an approach to build a low cost 3D PIV system for sub sonic wind tunnel applications as well as the related basic CFD studies. [Preview Abstract] |
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C1.00014: Metallic Nanoporous Films Fabricated by Etching Shilpa Chava, Julia Tilles, Wei Jiang Yeh Nanoporous metal films possess unique surface, structural, and bulk properties that underlie their importance in a wide range of applications such as catalysis, sensing, microfluidic control and filtration. In this presentation, we report our preliminary experimental results of metallic porous materials obtained by dealloying. The purpose of this research is to develop new strategies and techniques for the fabrication of nanoporous structures by selective chemical etching of different alloys. We have investigated two different chemical reactions: one is gold nanoporous films obtained from dissolving the silver component from the silver-gold alloy and the other is lead porous material obtained by etching out tin from lead-tin alloy. It was found that after dissolving the silver component, the remaining atoms gather together in clusters creating a rough surface, thereby causing the gold to evolve into porous material. We were able to tune the size of porous from about 10nm up to few 100 nm. When tin was etched off from lead-tin sheets, different microstructures were found by etching at different times. When it was etched for a short period of time, needle shaped structures with size of about a few 100's of nm were found. As we increased etching time, grain shaped structures were formed. [Preview Abstract] |
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