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Iowa State University

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2008

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Articles 1 - 30 of 47

Full-Text Articles in Physics

Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au Plus Au Collisions At Root S-Nn=200 Gev And Constraints On Medium Transport Coefficients, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Dec 2008

Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au Plus Au Collisions At Root S-Nn=200 Gev And Constraints On Medium Transport Coefficients, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

For Au + Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, p(T), up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 < p(T) < 20 GeV/c. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e. g., <(q) over cap > in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au + Au collisions.


Magnetic Domains In Magnetostrictive Fe–Ga Alloys, Qingfeng Xing, Thomas A. Lograsso Nov 2008

Magnetic Domains In Magnetostrictive Fe–Ga Alloys, Qingfeng Xing, Thomas A. Lograsso

Ames Laboratory Publications

Lorentz microscopy was applied to the observation of magnetic domains in iron-gallium (Fe–Ga) alloys. Results did not show any link between the magnetic domains and the magnetostriction enhancement by Ga addition, but did reveal that the drastic decrease in magnetostriction for Fe–31.2 at. % Ga was due to the presence of large scale precipitates. Magnetic domain features did not change in the alloys of A2, D03, A2+D03,A2+B2+D03, and A2+fine scale precipitates. Large scale precipitates within the slow-cooled Fe–31.2 at. % Ga affected both the distribution and wall motion of ...


Energetics Of Nonequilibrium Solidification In Al-Sm, Shihuai Zhou, Ralph E. Napolitano Nov 2008

Energetics Of Nonequilibrium Solidification In Al-Sm, Shihuai Zhou, Ralph E. Napolitano

Materials Science and Engineering Publications

Solution-based thermodynamic modeling, aided by first-principles calculations, is employed here to examine phase transformations in the Al-Sm binary system which may give rise to product phases that are metastable or have a composition that deviates substantially from equilibrium. In addition to describing the pure undercooled Al liquid with a two-state model that accounts for structural ordering, thermodynamic descriptions of the fcc phase, and intermediate compounds (Al4Sm-β, Al11Sm3-α, Al3Sm-δ, and Al2Sm-σ) are reanalyzed using special quasirandom structure and first-principles calculations. The possible phase compositions are presented over a range of temperatures using a “Baker-Cahn” analysis of the energetics of solidification and ...


Growth Of Bi Thin Films On Quasicrystal Surfaces, H. R. Sharma, V. Fournée, M. Shimoda, A. R. Ross, Thomas A. Lograsso, P. Gille, A. P. Tsai Oct 2008

Growth Of Bi Thin Films On Quasicrystal Surfaces, H. R. Sharma, V. Fournée, M. Shimoda, A. R. Ross, Thomas A. Lograsso, P. Gille, A. P. Tsai

Ames Laboratory Publications

We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral (i)-Al-Cu-Fe and i-Al-Pd-Mn and the tenfold surface of decagonal (d)-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage (θ) ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for θ≤1. For 1<θ<5, it forms nanocrystallites with (100) surface orientation. The islands have magic heights, which correspond to the stacking of four atomic layers (predominantly). The selection of magic heights is interpreted in terms of quantum size effects arising from the electron confinement within the film thickness. The islands establish rotational epitaxial relationship with the substrate. For higher coverage, the film grows with monatomic height, not with magic heights, and reflects the symmetry of the bulk Bi. When deposition is performed at 525 K, terrace diffusion is more effective, resulting in the aggregation of Bi adatoms developing into a smooth monolayer with quasiperiodic order. At this temperature, multilayers do not adsorb.


Characterization Of New Infrared Nonlinear Optical Material With High Laser Damage Threshold, Li2ga2ges6, Youngsik Kim, Inseok Seo, Steve W. Martin, Jaewook Baek, P. Shiv Halasyamani, Nachiappan Arumugam, Hugo Steinfink Oct 2008

Characterization Of New Infrared Nonlinear Optical Material With High Laser Damage Threshold, Li2ga2ges6, Youngsik Kim, Inseok Seo, Steve W. Martin, Jaewook Baek, P. Shiv Halasyamani, Nachiappan Arumugam, Hugo Steinfink

Materials Science and Engineering Publications

A new thio-germanium sulfide Li2Ga2GeS6 has been synthesized for the first time and its structure was found to be isomorphous with AgGaGeS4, which is well-known as a promising infrared NLO material. The host structure is built of GaS4 tetrahedra linked by corners to GeS4 tetrahedra to create a 3D framework forming tunnels along the c-axis, in which the Li+ions are located. The second harmonic generation (SHG) efficiency determined on powders of Li2Ga2GaS6 is 200 times larger than that of α-SiO2. Unlike AgGaS2 and AgGaGeS4, Li2Ga2GeS6 was observed to be very stable under prolonged Nd:YAG 1.064 μm ...


Onset Of Pi(0) Suppression Studied In Cu Plus Cu Collisions At Root S(Nn)=22.4, 62.4, And 200 Gev, Andrew Adare, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, S. Skutnik, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Oct 2008

Onset Of Pi(0) Suppression Studied In Cu Plus Cu Collisions At Root S(Nn)=22.4, 62.4, And 200 Gev, Andrew Adare, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, S. Skutnik, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Neutral pion transverse momentum (p(T)) spectra at midrapidity (|y| less than or similar to 0.35) were measured in Cu + Cu collisions at root s(NN) = 22.4, 62.4, and 200 GeV. Relative to pi(0) yields in p + p collisions scaled by the number of inelastic nucleon-nucleon collisions (N-coll) the pi(0) yields for p(T) greater than or similar to 2 GeV/c in central Cu + Cu collisions are suppressed at 62.4 and 200 GeV whereas an enhancement is observed at 22.4 GeV. A comparison with a jet-quenching model suggests that final state parton ...


Charged Hadron Multiplicity Fluctuations In Au+Au And Cu+Cu Collisions From Root S-Nn = 22.5 To 200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration Oct 2008

Charged Hadron Multiplicity Fluctuations In Au+Au And Cu+Cu Collisions From Root S-Nn = 22.5 To 200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration

Physics and Astronomy Publications

A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at s(NN)=62.4 and 200 GeV, and Cu+Cu collisions at s(NN)=22.5,62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or ...


Approximating A Three-Dimensional Fluidized Bed With Two-Dimensional Simulations, Mirka Deza, Francine Battaglia, Theodore J. Heindel Oct 2008

Approximating A Three-Dimensional Fluidized Bed With Two-Dimensional Simulations, Mirka Deza, Francine Battaglia, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Modeling these reactors with computational fluid dynamics (CFD) simulations is advantageous when performing parametric studies for design and scale-up. From a computational resource point of view, two-dimensional simulations are easier to perform than three-dimensional simulations, but they may not capture the proper physics. This paper will compare two- and three-dimensional simulations in a 10.2 cm diameter fluidized bed with side air injection to determine when two-dimensional simulations are adequate to capture the bed hydrodynamics ...


Simulating Gas-Liquid Flows In An External Loop Airlift Reactor, Deify Law, Francine Battaglia, Theodore J. Heindel Oct 2008

Simulating Gas-Liquid Flows In An External Loop Airlift Reactor, Deify Law, Francine Battaglia, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are connected with two horizontal connectors. Airlift reactors are utilized in fermentation processes and are preferred over traditional bubble column reactors because they can operate over a wider range of conditions. Computational fluid dynamics (CFD) simulations can be used to enhance our understanding of the hydrodynamics within these reactors. In the present work, the gas-liquid flow dynamics in an external loop airlift reactor are simulated using CFDLib with an Eulerian-Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems ...


J/Psi Production In Root S(Nn)=200 Gev Cu+Cu Collisions, Andrew Adare, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Sep 2008

J/Psi Production In Root S(Nn)=200 Gev Cu+Cu Collisions, Andrew Adare, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Yields for J/psi production in Cu+Cu collisions at root s(NN) = 200 GeV have been measured over the rapidity range |y|< 2.2 and compared with results in p+p and Au+Au collisions at the same energy. The Cu+Cu data offer greatly improved precision over existing Au+Au data for J/psi production in collisions with small to intermediate numbers of participants, in the range where the quark-gluon plasma transition threshold is predicted to lie. Cold nuclear matter estimates based on ad hoc fits to d+Au data describe the Cu+Cu data up to N-part similar to 50, corresponding to a Bjorken energy density of at least 1.5 GeV/fm(3).


Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman Aug 2008

Magnetic Structure Of Dy3+ In Hexagonal Multiferroic Dymno3, Shibabrata Nandi, Andreas Kreyssig, J.-Q. Yan, Matthew D. Vannette, J. C. Lang, L. Tan, J. W. Kim, Ruslan Prozorov, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

Element specific x-ray resonant magnetic scattering (XRMS) investigations were undertaken to determine the magnetic structure of the multiferroic compound, hexagonal DyMnO3. In the temperature range from 68 K down to 8 K the Dy3+ moments are aligned and antiferromagnetically correlated in the c direction according to the magnetic representation Γ3. The temperature dependence of the observed intensity can be modeled assuming the splitting of ground-state doublet crystal-field levels of Dy3+ by the exchange field of Mn3+. XRMS together with magnetization measurements indicate that the magnetic representation is Γ2 below 8 K.


Nucleation And Growth Of A Quasicrystalline Monolayer: Bi Adsorption On The Fivefold Surface Of I-Al70pd21mn9, J. A. Smerdon, J. K. Parle, L. H. Wearing, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Aug 2008

Nucleation And Growth Of A Quasicrystalline Monolayer: Bi Adsorption On The Fivefold Surface Of I-Al70pd21mn9, J. A. Smerdon, J. K. Parle, L. H. Wearing, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of i-Al70Pd21Mn9. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 Å is observed. The clusters have a common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density ...


Particle-Species Dependent Modification Of Jet-Induced Correlations In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Aug 2008

Particle-Species Dependent Modification Of Jet-Induced Correlations In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Measurements in Au + Au collisions at root s(NN) = 200 GeV of jet correlations for a trigger hadron at intermediate transverse momentum (p(T,trig)) with associated mesons or baryons at lower p(T,assoc) indicate strong modification of the away-side jet. The ratio of jet-associated baryons to mesons increases with centrality and p(T,assoc). For the most central collisions, the ratio is similar to that for inclusive measurements. This trend is incompatible with in-vacuum fragmentation but could be due to jetlike contributions from correlated soft partons, which recombine upon hadronization.


A Validation Study For The Hydrodynamics Of Biomass In A Fluidized Bed, Mirka Deza, Francine Battaglia, Theodore J. Heindel Aug 2008

A Validation Study For The Hydrodynamics Of Biomass In A Fluidized Bed, Mirka Deza, Francine Battaglia, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work focused on computational simulations of a fluidized bed using a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. Hydrodynamic results from the simulations were quantitatively compared with X-ray flow visualization studies of a similar bed. It was found that the Gidaspow model can accurately predict the hydrodynamics of the biomass in a fluidized bed. The coefficient of restitution of biomass was fairly high and did not affect the hydrodynamics of the bed ...


Minimum Fluidization Velocity And Gas Holdup In Fluidized Beds With Side Port Air Injection, Nathan P. Franka, Joshua B. Drake, Theodore J. Heindel Aug 2008

Minimum Fluidization Velocity And Gas Holdup In Fluidized Beds With Side Port Air Injection, Nathan P. Franka, Joshua B. Drake, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 cm and 15.2 cm diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum ...


Magnetic Phase Transitions And Ferromagnetic Short-Range Correlations In Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Jul 2008

Magnetic Phase Transitions And Ferromagnetic Short-Range Correlations In Single-Crystal Tb5si2.2ge1.8, Min Zou, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

Magnetic phase transitions in a Tb5Si2.2Ge1.8 single crystal have been studied as a function of temperature and magnetic field. Magnetic-field dependencies of the critical temperatures are highly anisotropic for both the main magnetic ordering process occurring around 120 K and a spin reorientation transition at ∼70 K. Magnetic-field-induced phase transitions occur with the magnetic field applied isothermally along the a and b axes (but not along the c axis) between 1.8 and 70 K in fields below 70 kOe. Strong anisotropic thermal irreversibility is observed in the Griffiths phase regime between 120 ...


Pressure Induced Superconductivity In Cafe2as2, Milton S. Torikachvili, Sergey L. Bud'ko, Ni Ni, Paul C. Canfield Jul 2008

Pressure Induced Superconductivity In Cafe2as2, Milton S. Torikachvili, Sergey L. Bud'ko, Ni Ni, Paul C. Canfield

Ames Laboratory Publications

CaFe2As2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasing to above 300 K by 19 kbar. A low temperature, superconducting dome (Tc∼12  K) is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears ...


Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield Jul 2008

Structural Transition And Anisotropic Properties Of Single-Crystalline Srfe2as2, J.-Q. Yan, Andreas Kreyssig, Shibabrata Nandi, N. Ni, Sergey L. Bud'ko, Robert J. Mcqueeney, R. William Mccallum, Thomas A. Lograsso, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

Platelike single crystals of SrFe2As2 as large as 3×3×0.5 mm3 have been grown out of Sn flux. The SrFe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at To=198 K, and do not show any sign of superconductivity down to 1.8 K. The structural transition is accompanied by an anomaly in the electrical resistivity, Hall resistivity, specific heat, and the anisotropic magnetic susceptibility. In an intermediate temperature range from 198 to 160 K, single-crystal x-ray diffraction suggests a coexistence ...


Dihadron Azimuthal Correlations In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jul 2008

Dihadron Azimuthal Correlations In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Azimuthal angle (Delta phi) correlations are presented for a broad range of transverse momentum (0.4 < p(T) < 10 GeV/c) and centrality (0-92%) selections for charged hadrons from dijets in Au+Au collisions at root s(NN) = 200 GeV. With increasing p(T), the away-side Delta phi distribution evolves from a broad and relatively flat shape to a concave shape, then to a convex shape. Comparisons with p + p data suggest that the away-side distribution can be divided into a partially suppressed "head" region centered at Delta phi similar to pi, and an enhanced "shoulder" region centered at Delta phi similar to pi +/- 1.1. The p(T) spectrum for the associated hadrons in the head region softens toward central collisions. The spectral slope for the shoulder region is independent of centrality and trigger p(T). The properties of the near-side distributions are also modified relative to those in p + p collisions, reflected by the broadening of the jet shape in Delta phi and Delta eta, and an enhancement of the per-trigger yield. However, these modifications seem to be limited to p(T)less than or similar to 4 GeV/c, above which both the hadron pair shape and per-trigger yield become similar to p + p collisions. These observations suggest that both the away- and near-side distributions contain a jet fragmentation component which dominates for p(T) greater than or similar to 5 GeV/c and a medium-induced component which is important for p(T) less than or similar to 4 GeV/c. We also quantify the role of jets at intermediate and low p(T) through the yield of jet-induced pairs in comparison with binary scaled p + p pair yield. The yield of jet-induced pairs is suppressed at high pair proxy energy (sum of the p(T) magnitudes of the two hadrons) and is enhanced at low pair proxy energy. The former is consistent with jet quenching; the latter is consistent with the enhancement of soft hadron pairs due to transport of lost energy to lower p(T).


Self-Consistent Swept Frequency Eddy Current Measurements For Characterization Of Near Surface Material Conditions, Chester C.H. Lo, Anatoli M. Frishman, Y. Shen, Norio Nakagawa Jul 2008

Self-Consistent Swept Frequency Eddy Current Measurements For Characterization Of Near Surface Material Conditions, Chester C.H. Lo, Anatoli M. Frishman, Y. Shen, Norio Nakagawa

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

This paper reports on a self‐consistent, swept frequency eddy current (SFEC) technique for characterizing surface and sub‐surface conditions of materials, with specific applications to detecting residual stresses in shot‐peened Ni‐base superalloys and surface oxidation in engineering components. The technique involves measuring lift‐off normalized vertical component signal to suppress lift off noise and instrumentation effect. Theoretical study shows that the vertical component signals are insensitive to coil dimensions, thus enabling EC measurements in separate frequency bands using multiple coils, while yielding continuous broad‐band data so that both the bulk conductivity and near‐surface conductivity profile ...


A Scaling Law For Nondestructive Evaluation Of Shot Peening Induced Surface Material Property Deviations, Anatoli M. Frishman, Chester C.H. Lo, Y. Shen, Norio Nakagawa Jul 2008

A Scaling Law For Nondestructive Evaluation Of Shot Peening Induced Surface Material Property Deviations, Anatoli M. Frishman, Chester C.H. Lo, Y. Shen, Norio Nakagawa

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

Shot peening is frequently used to improve mechanical characteristics of metallic components’ surfaces. The physical properties of shot peened surfaces exhibit deviations from their bulk values. This paper shows that there exists a scaling law (universality) among seemingly unrelated material property deviations and among different peening conditions. We present examples and support for scaling behaviors based on experimental data on Almen strip deflection, cold work and residual stress profiles of a shot peened nickel‐base superalloy (Waspaloy), and swept frequency eddy current signals used for NDE studies of another shot peened nickel‐base superalloy (Inconel 718). In addition, a fast ...


Shot-Peening Intensities Vs. Eddy Current Signals As Seen In Iterative Treatment-Measurement Experiment, Norio Nakagawa, Anatoli M. Frishman, Y. Shen, Chester C.H. Lo Jul 2008

Shot-Peening Intensities Vs. Eddy Current Signals As Seen In Iterative Treatment-Measurement Experiment, Norio Nakagawa, Anatoli M. Frishman, Y. Shen, Chester C.H. Lo

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

We report on progress in a swept high frequency eddy current (SHFEC) technique for characterization of surface residual stress on shot‐peened superalloy surfaces. Our aim here is to demonstrate the sensitivity of our measurement for practical shot peening intensities, i.e. at 4 ∼ 6 A. First, we present our improved probe and instrumentation being sufficiently sensitive to resolve the surface conditions at these low Almen intensities, where our earlier measurements encountered noise problems. The previous coil was also larger (18 mm in diameter) than desirable. Our new probe integrates smaller coils (12 mm in diameter, forming an AC bridge ...


Polarized Thermal Radiation By Layer-By-Layer Metallic Emitters With Sub-Wavelength Grating, Jae-Hwang Lee, Wai Y. Leung, Tae Guen Kim, Kristen P. Constant, Kai-Ming Ho Jun 2008

Polarized Thermal Radiation By Layer-By-Layer Metallic Emitters With Sub-Wavelength Grating, Jae-Hwang Lee, Wai Y. Leung, Tae Guen Kim, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 µm, as well as high emissivity up to 0.65 at a wavelength of 3.7µm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by ...


Source Breakup Dynamics In Au+Au Collisions At Root S(Nn)=200 Gev Via Three-Dimensional Two-Pion Source Imaging, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jun 2008

Source Breakup Dynamics In Au+Au Collisions At Root S(Nn)=200 Gev Via Three-Dimensional Two-Pion Source Imaging, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

A three-dimensional correlation function obtained from midrapidity, low p(T), pion pairs in central Au+Au collisions at root s(NN) = 200 GeV is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). A proper breakup time tau(0) similar to 9 fm/c and a mean proper emission duration Delta tau similar to 2 fm/c, leading to sizable emission time differences ( approximate to 12 fm/c), are required to allow models to be successfully matched to these tails. The model comparisons also ...


Quantitative Constraints On The Transport Properties Of Hot Partonic Matter From Semi-Inclusive Single High Transverse Momentum Pion Suppression In Au Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jun 2008

Quantitative Constraints On The Transport Properties Of Hot Partonic Matter From Semi-Inclusive Single High Transverse Momentum Pion Suppression In Au Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment has measured the suppression of semi-inclusive single high-transverse-momentum pi(0)'s in Au+Au collisions at root s(NN) = 200 GeV. The present understanding of this suppression is in terms of energy loss of the parent (fragmenting) parton in a dense color-charge medium. We have performed a quantitative comparison between various parton energy-loss models and our experimental data. The statistical point-to-point uncorrelated as well as correlated systematic uncertainties are taken into account in the comparison. We detail this methodology and the resulting constraint on the model parameters, such as the initial color-charge density dN(g)/dy, the ...


Self-Assembly, Structure, And Electronic Properties Of A Quasiperiodic Lead Monolayer, J. Ledieu, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée Feb 2008

Self-Assembly, Structure, And Electronic Properties Of A Quasiperiodic Lead Monolayer, J. Ledieu, L. Leung, L. H. Wearing, R. Mcgrath, Thomas A. Lograsso, D. Wu, V. Fournée

Ames Laboratory Publications

A quasiperiodic Pb monolayer has been formed on the fivefold surface of the Al-Pd-Mn quasicrystal. Growth of the monolayer proceeds via self-assembly of an interconnected network of pentagonal Pb stars, which are shown to be τ inflated compared to similar structural elements of the quasiperiodic substrate. Measurements of the electronic structure of the system using scanning tunneling spectroscopy and ultraviolet photoemission spectroscopy reveal that the Pb monolayer displays a pseudogap at the Fermi level which is directly related to its quasiperiodic structure.


Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman Feb 2008

Spin-Flop Transition In Gd5ge4 Observed By X-Ray Resonant Magnetic Scattering And First-Principles Calculations Of Magnetic Anisotropy, L. Tan, Andreas Kreyssig, Shibabrata Nandi, S. Jia, Yongbin Lee, J. C. Lang, Z. Islam, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Paul C. Canfield, Bruce N. Harmon, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd5Ge4 and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90° from the c axis to the a axis when a magnetic field, Hsf=9 kOe, is applied along the c axis at T=9 K. The magnetic space group changes from Pnm′a to Pn′m′a′ for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the ...


Cold Nuclear Matter Effects On J/Psi Production As Constrained By Deuteron-Gold Measurements At Root S-Nn=200 Gev, Andrew Adare, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration Feb 2008

Cold Nuclear Matter Effects On J/Psi Production As Constrained By Deuteron-Gold Measurements At Root S-Nn=200 Gev, Andrew Adare, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present a new analysis of J/psi production yields in deuteron-gold collisions at root s(NN) =200 GeV using data taken from the PHENIX experiment in 2003 and previously published in S. S. Adler [Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 are used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors (R-dAu). A suppression of J/psi in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial-state low-x gluons in ...


Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle Jan 2008

Effect Of Interstitial Additions On Magnetostriction In Fe–Ga Alloys, Mianliang Huang, Thomas A. Lograsso, A. E. Clark, J. B. Restorff, M. Wun-Fogle

Ames Laboratory Conference Papers, Posters, and Presentations

The additions of trace amounts of small interstitial atoms (carbon, boron, and nitrogen) to Fe–Ga (Galfenol) alloys have a small but beneficial effect on the magnetostriction of Fe–Ga alloys especially at high Ga compositions. The saturated magnetostrictions [(3/2)λ100’s] of both slow cooled and quenched single crystal Fe–Ga–C alloys with Ga contents >18 at. % are about 10%–30% higher than those of the comparable binary Fe–Ga alloys. For boron and nitrogen additions, the magnetostrictions of slow cooled alloys with Ga content >18 at. % were approximately 20% higher than those of the binary ...


Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso Jan 2008

Temperature Dependence Of The Magnetostriction And Magnetoelastic Coupling In Fe100−Xalx (X = 14.1,16.6,21.5,26.3) And Fe50co50, A. E. Clark, J. B. Restorff, M. Wun-Fogle, D. Wu, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper, we report magnetostriction measurements, (λ100) on Fe-rich Fe–Al alloys and Fe50Co50 as functions of temperature from 77 K to room temperature (RT). From these measurements and elastic constant (c′) measurements, the tetragonal magnetoelastic coupling constants (b1’s) were calculated. Significant differences were found between our RT measurements and earlier magnetostriction measurements for the higher Al concentration alloys (16.6%, 21.5%, 26.3% Al) and the Fe50Co50 alloy. Reminiscent of the temperature dependence of λ100 for pure Fe, magnetostriction changes with temperature are minimal for Fe–Al ...