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Iowa State University

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2010

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Articles 1 - 30 of 52

Full-Text Articles in Physics

Measurement Of Transverse Single-Spin Asymmetries For J/Psi Production In Polarized P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Dec 2010

Measurement Of Transverse Single-Spin Asymmetries For J/Psi Production In Polarized P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report the first measurement of transverse single-spin asymmetries in J/psi production from transversely polarized p + p collisions at root s = 200 GeV with data taken by the PHENIX experiment in 2006 and 2008. The measurement was performed over the rapidity ranges 1.2 < vertical bar y vertical bar < 2.2 and vertical bar y vertical bar < 0.35 for transverse momenta up to 6 GeV/c. J/psi production at the Relativistic Heavy Ion Collider is dominated by processes involving initial-state gluons, and transverse single-spin asymmetries of the J/psi can provide access to gluon dynamics within the nucleon. Such asymmetries may also shed light on the long-standing question in QCD of the J/psi production mechanism. Asymmetries were obtained as a function of J/psi transverse momentum and Feynman-x, with a value of -0.086 +/- 0.026(stat) +/- 0.003(syst) in the forward region. This result suggests possible nonzero trigluon correlation functions in transversely polarized protons and, if well defined in this reaction, a nonzero gluon Sivers distribution function.


In Situ Observation Of Antisite Defect Formation During Crystal Growth, Matthew J. Kramer, Mikhail I. Mendelev, Ralph E. Napolitano Dec 2010

In Situ Observation Of Antisite Defect Formation During Crystal Growth, Matthew J. Kramer, Mikhail I. Mendelev, Ralph E. Napolitano

Materials Science and Engineering Publications

In situ x-ray diffraction (XRD) coupled with molecular dynamics (MD) simulations have been used to quantify antisite defect trapping during crystallization. Rietveld refinement of the XRD data revealed a marked lattice distortion which involves an a axis expansion and a c axis contraction of the stable C11b phase. The observed lattice response is proportional in magnitude to the growth rate, suggesting that the behavior is associated with the kinetic trapping of lattice defects. MD simulations demonstrate that this lattice response is due to incorporation of 1% to 2% antisite defects during growth.


Modulation On Ni2mnga(001) Surface, S. W. D'Souza, Abhishek Rai, J. Nayak, M. Maniraj, R. S. Dhaka, S. R. Barman, Deborah L. Schlagel, Thomas A. Lograsso Dec 2010

Modulation On Ni2mnga(001) Surface, S. W. D'Souza, Abhishek Rai, J. Nayak, M. Maniraj, R. S. Dhaka, S. R. Barman, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

We report periodic modulation on (001) surface of Ni2MnGa ferromagnetic shape memory alloy. For the stoichiometric surface, analysis of the low energy electron diffraction (LEED) spot profiles shows that the modulation is incommensurate. The modulation appears at 200 K, concomitant with the first order structural transition to the martensitic phase.


Two- And Three-Dimensional Growth Of Bi On I-Al-Pd-Mn Studied Using Medium-Energy Ion Scattering, T. C. Q. Noakes, P. Bailey, C. F. Mcconville, M. Draxler, M. Walker, M. G. Brown, A. Hentz, D. P. Woodruff, Thomas A. Lograsso, A. R. Ross, J. A. Smerdon, L. Leung, R. Mcgrath Nov 2010

Two- And Three-Dimensional Growth Of Bi On I-Al-Pd-Mn Studied Using Medium-Energy Ion Scattering, T. C. Q. Noakes, P. Bailey, C. F. Mcconville, M. Draxler, M. Walker, M. G. Brown, A. Hentz, D. P. Woodruff, Thomas A. Lograsso, A. R. Ross, J. A. Smerdon, L. Leung, R. Mcgrath

Ames Laboratory Publications

Recent work on the growth of thin metal films on quasicrystalline substrates has indicated the formation of so-called “magic height” islands with multiples of 4 atomic layers (AL) arising as a result of quantum size effects, which lead to enhanced stability. Here the results of a study are reported of Bi deposition on i-Al-Pd-Mn using medium-energy ion scattering to characterize the island thickness and the structural arrangement of Bi atoms within the islands. In addition, data were taken from annealed surfaces after Bi cluster desorption to leave a single aperiodic monolayer of Bi at the surface. Scattered-ion energy spectra from ...


Thermoelectric Power Investigations Of Ybagge Across The Quantum Critical Point, Eundeok Mun, Sergey L. Bud'ko, Paul C. Canfield Nov 2010

Thermoelectric Power Investigations Of Ybagge Across The Quantum Critical Point, Eundeok Mun, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

The magnetic field and temperature dependences of the thermoelectric power (TEP) of the antiferromagnetically ordered heavy fermion compound YbAgGe are measured across the field-induced quantum critical point. These TEP measurements reproduce the earlier H-T phase diagram and identify an additional domelike phase between ∼45and ∼70 kOe. On the low-field side of this region, H>Hc∼45 kOe, the sign of the TEP changes from negative to positive; on the high-field side of this region, H≈70 kOe, a non-Fermi-liquid state is evidenced as the logarithmic temperature dependence of S(T)/T, in agreement with previous specific heat results C(T ...


Rapidity And Centrality Dependence Of Azimuthal Correlations In Deuteron-Gold Collisions At Rhic, Kirill Tuchin Nov 2010

Rapidity And Centrality Dependence Of Azimuthal Correlations In Deuteron-Gold Collisions At Rhic, Kirill Tuchin

Physics and Astronomy Publications

We calculate azimuthal correlations in dAu collisions at different rapidities and centralities and argue that experimentally observed depletion of the back-to-back pick can be quantitatively explained by gluon saturation in the Color Glass Condensate of the Gold nucleus.


Compositional Disorder, Polar Nanoregions And Dipole Dynamics In Pb(Mg1/3nb2/3)O3-Based Relaxor Ferroelectrics, Alexei A. Bokov, Brian J. Rodriguez, Xiaohui Zhao, Jae-Hyeon Ko, Stephen Jesse, Xifa Long, Weiguo Qu, Tae Hyun Kim, John D. Budai, Anna N. Morozovska, Seiji Kojima, Xiaoli Tan, Sergei V. Kalinin, Zuo-Guang Ye Nov 2010

Compositional Disorder, Polar Nanoregions And Dipole Dynamics In Pb(Mg1/3nb2/3)O3-Based Relaxor Ferroelectrics, Alexei A. Bokov, Brian J. Rodriguez, Xiaohui Zhao, Jae-Hyeon Ko, Stephen Jesse, Xifa Long, Weiguo Qu, Tae Hyun Kim, John D. Budai, Anna N. Morozovska, Seiji Kojima, Xiaoli Tan, Sergei V. Kalinin, Zuo-Guang Ye

Materials Science and Engineering Publications

The complex structure of relaxor ferroelectrics comprises polar nanoregions (PNRs) which appear upon cooling below the Burns temperature and quenched compositional (chemical) disorder. The relation between the polar nanostructure and compositionally ordered regions (CORs) often observed in relaxors has been the subject of extensive theoretical investigations; however, the experimental data, especially concerning Pb(B′1/3B″2/3)O3-type complex perovskite relaxors, are rather limited. In this paper, we analyse and discuss the results of our recent investigations of the morphology of CORs and the dynamics of PNRs in Pb(Mg1/3Nb2/3)O3 based solid solutions in which the ...


Elastic, Thermodynamic, And Electronic Properties Of Mnsi, Fesi, And Cosi, Alla E. Petrova, V. N. Krasnorussky, Anatoly A. Shikov, William M. Yuhasz, Thomas A. Lograsso, Jason C. Lashley, Sergei M. Stishov Oct 2010

Elastic, Thermodynamic, And Electronic Properties Of Mnsi, Fesi, And Cosi, Alla E. Petrova, V. N. Krasnorussky, Anatoly A. Shikov, William M. Yuhasz, Thomas A. Lograsso, Jason C. Lashley, Sergei M. Stishov

Ames Laboratory Publications

Measurements of the sound velocities, heat capacities, magnetic susceptibilities, and electrical resistivities of single crystals of MnSi, FeSi, and CoSi were performed in the temperature range 2.5–300 K and the elastic constants were calculated. The temperature dependence of the mentioned quantities reveals nontrivial features, reflecting specifics of magnetic and electron subsystems in these materials.


Structural Phase Transition And Superlattice Misfit Strain Of Rfeaso (R=La, Pr, Nd, Sm), A. Ricci, N. Poccia, B. Joseph, L. Barba, G. Arrighetti, G. Clasca, J.-Q. Yan, R. William Mccallum, Thomas A. Lograsso, N. D. Zhigadlo, J. Karpinsky, A. Bianconi Oct 2010

Structural Phase Transition And Superlattice Misfit Strain Of Rfeaso (R=La, Pr, Nd, Sm), A. Ricci, N. Poccia, B. Joseph, L. Barba, G. Arrighetti, G. Clasca, J.-Q. Yan, R. William Mccallum, Thomas A. Lograsso, N. D. Zhigadlo, J. Karpinsky, A. Bianconi

Ames Laboratory Publications

The tetragonal-to-orthorhombic structural phase transition (SPT) in LaFeAsO (La-1111) and SmFeAsO (Sm-1111) single crystals measured by high-resolution x-ray diffraction is found to be sharp while the RFeAsO (R=La, Nd, Pr, Sm) polycrystalline samples show a broad continuous SPT. Comparing the polycrystalline and the single-crystal 1111 samples, the critical exponents of the SPT are found to be the same while the correlation length critical exponents are found to be very different. These results imply that the lattice fluctuations in 1111 systems change in samples with different surface to volume ratio that is assigned to the relieve of the temperature-dependent superlattice ...


High P(T) Direct Photon And Pi(0) Triggered Azimuthal Jet Correlations And Measurement Of K(T) For Isolated Direct Photons In P Plus P Collisions At Root S=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 2010

High P(T) Direct Photon And Pi(0) Triggered Azimuthal Jet Correlations And Measurement Of K(T) For Isolated Direct Photons In P Plus P Collisions At Root S=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

Correlations of charged hadrons of 1< p(T) < 10 Gev/c with high pT direct photons and pi(0) mesons in the range 5< p(T) < 15 Gev/c are used to study jet fragmentation in the gamma + jet and dijet channels, respectively. The magnitude of the partonic transverse momentum, k(T), is obtained by comparing to a model incorporating a Gaussian kT smearing. The sensitivity of the associated charged hadron spectra to the underlying fragmentation function is tested and the data are compared to calculations using recent global fit results. The shape of the direct photon-associated hadron spectrum as well as its charge asymmetry are found to be consistent with a sample dominated by quark-gluon Compton scattering. No significant evidence of fragmentation photon correlated production is observed within experimental uncertainties.


Stochastic Coarsening Model For Pb Islands On A Si(111) Surface, G. P. Zhang, Myron Hupalo, M. Li, C. Z. Wang, James W. Evans, Michael C. Tringides, K. M. Ho Oct 2010

Stochastic Coarsening Model For Pb Islands On A Si(111) Surface, G. P. Zhang, Myron Hupalo, M. Li, C. Z. Wang, James W. Evans, Michael C. Tringides, K. M. Ho

Physics and Astronomy Publications

The coarsening behavior of individual Pb islands on Si(111) surface has been studied by scanning tunneling microscopy. Traditionally island decay follows a smooth power-law dependence on the time until disappearance. In Pb/Si(111), some unstable islands are inactive for a long time but once their decay is triggered they suffer a “sudden death.” Four-layer islands are found to decay rapidly, increasing the area covered by seven-layer islands. All islands, decaying or otherwise, are accompanied by island size fluctuation which involve a large number of perimeter atoms moving collectively as a “quantized” unit. A stochastic model is developed to ...


Azimuthal Anisotropy Of Pi(0) Production In Au Plus Au Collisions At Root S(Nn)=200 Gev: Path-Length Dependence Of Jet Quenching And The Role Of Initial Geometry, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Sep 2010

Azimuthal Anisotropy Of Pi(0) Production In Au Plus Au Collisions At Root S(Nn)=200 Gev: Path-Length Dependence Of Jet Quenching And The Role Of Initial Geometry, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We have measured the azimuthal anisotropy of pi(0) production for 1 < p(T) < 18 GeV/c for Au + Au collisions at root s(NN) = 200 GeV. The observed anisotropy shows a gradual decrease for 3 less than or similar to p(T) less than or similar to 7-10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is underpredicted, up to at least similar to 10 GeV/c, by current perturbative QCD (PQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than what is implied by current PQCD energy-loss models show reasonable agreement with the data.


Crystal-Field Excitations And Spin-Phonon Interactions In Dyni2b2c: Raman Scattering Study, Heesuk Rho, Miles V. Klein, Paul C. Canfield Aug 2010

Crystal-Field Excitations And Spin-Phonon Interactions In Dyni2b2c: Raman Scattering Study, Heesuk Rho, Miles V. Klein, Paul C. Canfield

Ames Laboratory Publications

We report polarized Raman results of magnetic superconductor DyNi2B2C (Tc=6.2 K, TN=10.3 K) to explore crystal-field (CF) excitations and spin-phonon interactions. In addition to the Ni-B1g phonon mode at 199 cm−1, we observed additional Raman modes at 124, 151, and 221 cm−1. By careful analysis of the temperature evolution of these modes, we attribute the 124 cm−1 excitation to a CF transition. The 151 and 221 cm−1 modes correspond to zone-folded phonons because they are completely quenched for T>TN. With increasing temperature across TN, the 124 cm−1 excitation diminishes rapidly ...


Surface-Driven Electronic Structure In Lafeaso Studied By Angle-Resolved Photoemission Spectroscopy, Chang Liu, Yongbin Lee, Ari D. Palczewski, J.-Q. Yan, Takeshi Kondo, Bruce N. Harmon, R. William Mccallum, Thomas A. Lograsso, Adam Kaminski Aug 2010

Surface-Driven Electronic Structure In Lafeaso Studied By Angle-Resolved Photoemission Spectroscopy, Chang Liu, Yongbin Lee, Ari D. Palczewski, J.-Q. Yan, Takeshi Kondo, Bruce N. Harmon, R. William Mccallum, Thomas A. Lograsso, Adam Kaminski

Ames Laboratory Publications

We measured the electronic structure of an iron arsenic parent compound LaFeAsO using angle-resolved photoemission spectroscopy (ARPES). By comparing with a full-potential linear augmented plane wave calculation we show that the extra large Γhole pocket measured via ARPES comes from electronic structure at the sample surface. Based on this we discuss the strong-polarization dependence of the band structure and a temperature-dependent holelike band around the M point. The two phenomena give additional evidences for the existence of the surface-driven electronic structure.


Interplay Of Fe And Nd Magnetism In Ndfeaso Single Crystals, W. Tian, W. Ratcliff Ii, M. G. Kim, J.-Q. Yan, P. A. Klenzle, Q. Huang, Brandt A. Jensen, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman, J. W. Lynn, Andreas Kreyssig Aug 2010

Interplay Of Fe And Nd Magnetism In Ndfeaso Single Crystals, W. Tian, W. Ratcliff Ii, M. G. Kim, J.-Q. Yan, P. A. Klenzle, Q. Huang, Brandt A. Jensen, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso, Robert J. Mcqueeney, Alan I. Goldman, J. W. Lynn, Andreas Kreyssig

Ames Laboratory Publications

The structural and magnetic phase transitions have been studied on NdFeAsO single crystals by neutron and x-ray diffraction complemented by resistivity and specific-heat measurements. Two low-temperature phase transitions have been observed in addition to the tetragonal-to-orthorhombic transition at TS∼142 K and the onset of antiferromagnetic (AFM) Fe order belowTN∼137 K. The Fe moments order AFM in the well-known stripelike structure in the (ab) plane but change from AFM to ferromagnetic (FM) arrangement along the c direction below T∗∼15 K accompanied by the onset of Nd AFM order below TNd∼6 K with this same ...


Electronic Structure And Lattice Dynamics Of The Magnetic Shape-Memory Alloy Co2niga, M. Siewert, M. E. Gruner, A. Dannenberg, A. Hucht, S. M. Shapiro, G. Xu, Thomas A. Lograsso, P. Entel Aug 2010

Electronic Structure And Lattice Dynamics Of The Magnetic Shape-Memory Alloy Co2niga, M. Siewert, M. E. Gruner, A. Dannenberg, A. Hucht, S. M. Shapiro, G. Xu, Thomas A. Lograsso, P. Entel

Ames Laboratory Publications

In addition to the prototypical Ni-Mn-based Heusler alloys, the Co-Ni-Ga systems have recently been suggested as another prospective materials class for magnetic shape-memory applications. We provide a characterization of the dynamical properties of this material and their relation to the electronic structure within a combined experimental and theoretical approach. This relies on inelastic neutron scattering to obtain the phonon dispersion while first-principles calculations provide the link between dynamical properties and electronic structure. In contrast to Ni2MnGa, where the softening of the TA2 phonon branch is related to Fermi-surface nesting, our results reveal that the respective anomalies are ...


Experimental Exploration Of The Origin Of Magnetostriction In Single Crystalline Iron, Qingfeng Xing, Thomas A. Lograsso, M. P. Ruffoni, C. Azimonte, S. Pascarelli, D. J. Miller Aug 2010

Experimental Exploration Of The Origin Of Magnetostriction In Single Crystalline Iron, Qingfeng Xing, Thomas A. Lograsso, M. P. Ruffoni, C. Azimonte, S. Pascarelli, D. J. Miller

Ames Laboratory Publications

The magnetostrictive atomic strain in a pure Fe single crystal was measured by differential x-ray absorption spectroscopy. The obtained tetragonal magnetostriction constant, (3/2)λ100, was determined to be 45 ppm, consistent with the previously reported theoretical value calculated from a spin-orbit coupling theory. These results provide a foundation for understanding the origin of magnetostriction in pure Fe as well as Fe-based binary alloys.


Phase Transitions And Iron-Ordered Moment Form Factor In Lafeaso, H.-F. Li, W. Tian, J.-Q. Yan, Jerel L. Zarestky, R. William Mccallum, Thomas A. Lograsso, David Vaknin Aug 2010

Phase Transitions And Iron-Ordered Moment Form Factor In Lafeaso, H.-F. Li, W. Tian, J.-Q. Yan, Jerel L. Zarestky, R. William Mccallum, Thomas A. Lograsso, David Vaknin

Ames Laboratory Publications

Elastic neutron-scattering studies of single-crystal LaFeAsO reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O) structural transition occurs at TS≈156 K, and it exhibits a sharp transition at TP≈148 K. We argue that in the temperature range TS to TP, T and O structures may dynamically coexist possibly due to nematic spin correlations recently proposed for the iron pnictides, and we attribute TP to the formation of long-range O domains from the finite local precursors. The antiferromagnetic structure emerges at TN≈140 K, with the iron moment direction along ...


Elliptic And Hexadecapole Flow Of Charged Hadrons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Aug 2010

Elliptic And Hexadecapole Flow Of Charged Hadrons In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Differential measurements of the elliptic (upsilon(2)) and hexadecapole (upsilon(4)) Fourier flow coefficients are reported for charged hadrons as a function of transverse momentum (p(T)) and collision centrality or number of participant nucleons (N-part) for Au + Au collisions at root s(NN) = 200 GeV/ The upsilon(2,4) measurements at pseudorapidity vertical bar eta vertical bar <= 0.35, obtained with four separate reaction-plane detectors positioned in the range 1.0 < vertical bar eta vertical bar < 3.9, show good agreement, indicating the absence of significant Delta eta-dependent nonflow correlations. Sizable values for upsilon(4)(p(T)) are observed with a ratio upsilon(4)(p(T), N-part)/upsilon(2)(2)(p(T), N-part) approximate to 0.8 for 50 less than or similar to N-part less than or similar to 200, which is compatible with the combined effects of a finite viscosity and initial eccentricity fluctuations. For N-part greater than or similar to 200 this ratio increases up to 1.7 in the most central collisions.


From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel Aug 2010

From Initial To Late Stages Of Epitaxial Thin Film Growth: Stm Analysis And Atomistic Or Coarsegrained Modeling, James W. Evans, Yong Han, Barış Ünal, Maozhi Li, K. J. Caspersen, Dapeng Jing, Anthony R. Layson, C. R. Stoldt, T. Duguet, Patricia A. Thiel

Chemistry Conference Papers, Posters and Presentations

Epitaxial thin film growth by vapor deposition or molecular beam epitaxy under ultra‐high vacuum conditions generally occurs in two stages: (i) nucleation and growth of well‐separated islands on the substrate; (ii) subsequent formation of a thicker continuous film with possible kinetic roughening. For homoepitaxial growth, two‐dimensional (2D) monolayer islands are formed during submonolayer deposition. Typically, the presence of a step‐edge barrier inhibits downward transport and leads to the formation of mounds (multilayer stacks of 2D islands) during multilayer growth. For heteroepitaxial growth, islands formed in the initial stages of deposition sometimes have a 2D monolayer structure ...


A Method To Quantify Mixing In A Two Component Fluidized Bed, Norman K. Keller, Theodore J. Heindel Aug 2010

A Method To Quantify Mixing In A Two Component Fluidized Bed, Norman K. Keller, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Fluidized bed technology can be used for pyrolysis and gasification of solid fuel particles such as biomass, which is important to industry because of its potential as an alternative for petroleum-based fuels. To efficiently utilize a fluidized bed reactor it is necessary, among other factors, to investigate the mixing and segregation behavior of the fuel particles with the bed material. In order to characterize the material distribution, a technique to visualize the biomass inside a fluidized bed reactor has been developed using X-ray computed tomography (CT) scans. This paper presents an image analysis procedure that can be used to quantify ...


Metastability In Schloegl’S Second Model For Autocatalysis: Lattice-Gas Realization With Particle Diffusion, Xiaofang Guo, Y. De Decker, James W. Evans Aug 2010

Metastability In Schloegl’S Second Model For Autocatalysis: Lattice-Gas Realization With Particle Diffusion, Xiaofang Guo, Y. De Decker, James W. Evans

Physics and Astronomy Publications

We analyze metastability associated with a discontinuous nonequilibrium phase transition in a stochastic lattice-gas realization of Schloegl’s second model for autocatalysis. This model realization involves spontaneous annihilation, autocatalytic creation, and diffusion of particles on a square lattice, where creation at empty sites requires an adjacent diagonal pair of particles. This model, also known as the quadratic contact process, exhibits discontinuous transition between a populated active state and a particle-free vacuum or “poisoned” state, as well as generic two-phase coexistence. The poisoned state exists for all particle annihilation rates p>0and hop rates h≥0 and is an absorbing state ...


Transverse Momentum Dependence Of Eta Meson Suppression In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Jul 2010

Transverse Momentum Dependence Of Eta Meson Suppression In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

New measurements by the PHENIX experiment at the Relativistic Heavy Ion Collider for. production at midrapidity as a function of transverse momentum ((PT)) and collision centrality in root s(NN) = 200 GeV Au + Au and p + p collisions are presented. They indicate nuclear modification factors (R-AA) which are similar in both magnitude and trend to those found in earlier pi(0) measurements. Linear fits to R-AA as a function of (PT) in 5-20 GeV/c show that the slope is consistent with zero within two standard deviations at all centralities, although a slow rise cannot be excluded. Having different statistical ...


Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Baris Unal, Dapeng Jing, Patricia A. Thiel, James W. Evans, Da-Jiang Liu Jul 2010

Nanoscale “Quantum” Islands On Metal Substrates: Microscopy Studies And Electronic Structure Analyses, Yong Han, Baris Unal, Dapeng Jing, Patricia A. Thiel, James W. Evans, Da-Jiang Liu

Physics and Astronomy Publications

Confinement of electrons can occur in metal islands or in continuous films grown heteroepitaxially upon a substrate of a different metal or on a metallic alloy. Associated quantum size effects (QSE) can produce a significant height-dependence of the surface free energy for nanoscale thicknesses of up to 10–20 layers. This may suffice to induce height selection during film growth. Scanning STM analysis has revealed remarkable flat-topped or mesa-like island and film morphologies in various systems. We discuss in detail observations of QSE and associated film growth behavior for Pb/Cu(111), Ag/Fe(100), and Cu/fcc-Fe/Cu(100 ...


Transverse Momentum Dependence Of J/Psi Polarization At Midrapidity In P Plus P Collisions At Root S=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Jul 2010

Transverse Momentum Dependence Of J/Psi Polarization At Midrapidity In P Plus P Collisions At Root S=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report the measurement of the transverse momentum dependence of inclusive J/psi polarization in p + p collisions at root s = 200 GeV performed by the PHENIX Experiment at the Relativistic Heavy Ion Collider. The J/psi polarization is studied in the helicity, Gottfried-Jackson, and Collins-Soper frames for p(T) < 5 GeV/c and vertical bar y vertical bar < 0.35. The polarization in the helicity and Gottfried-Jackson frames is consistent with zero for all transverse momenta, with a slight (1.8 sigma) trend towards longitudinal polarization for transverse momenta above 2 GeV/c. No conclusion is allowed due to the limited acceptance in the Collins-Soper frame and the uncertainties of the current data. The results are compared to observations for other collision systems and center of mass energies and to different quarkonia production models.


Transition In Yield And Azimuthal Shape Modification In Dihadron Correlations In Relativistic Heavy Ion Collisions, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Jun 2010

Transition In Yield And Azimuthal Shape Modification In Dihadron Correlations In Relativistic Heavy Ion Collisions, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Hard-scattered parton probes produced in collisions of large nuclei indicate large partonic energy loss, possibly with collective produced-medium response to the lost energy. We present measurements of pi(0) trigger particles at transverse momenta p(T)(t) = 4-12 GeV/c and associated charged hadrons (p(T)(a) = 0.5-7 GeV/c) vs relative azimuthal angle Delta phi in Au + Au and p + p collisions at root s(NN) = 200 GeV. The Au + Au distribution at low p(T)(a), whose shape has been interpreted as a medium effect, is modified for p(T)(t) < 7 GeV/c. At higher p(T)(t), the data are consistent with unmodified or very weakly modified shapes, even for the lowest measured p(T)(a), which quantitatively challenges some medium response models. The associated yield of hadrons opposing the trigger particle in Au + Au relative to p + p (I-AA) is suppressed at high p(T) (I-AA approximate to 0.35-0.5), but less than for inclusive suppression (R-AA approximate to 0.2).


Thermodynamic Limits Of Crystallization And The Prediction Of Glass Formation Tendency, Yongxin Yao, Ralph E. Napolitano, Cai-Zhuang Wang, Kai-Ming Ho Jun 2010

Thermodynamic Limits Of Crystallization And The Prediction Of Glass Formation Tendency, Yongxin Yao, Ralph E. Napolitano, Cai-Zhuang Wang, Kai-Ming Ho

Materials Science and Engineering Publications

We have calculated the T0 curves for several Al-rare-earth binary alloys to assess the importance of the transport-based resistance to crystallization in the overall glass formation process and the general effectiveness of thermodynamic prediction of glass-forming ability. Our results show that the experimentally observed glass-forming compositions for Al-(Ce, Gd, Ho, Nd, Y, Dy) alloys strongly correlate with the composition range bounded by the T0curves associated with the relevant crystalline phases. This indicates that sluggish material transport, together with the tendency for clustering and other types of ordering at medium-range scale, is a key factor governing glass formation in these ...


The Effect Of Partial Substitution Of Ge For Ga On The Elastic And Magnetoelastic Properties Of Fe–Ga Alloys, G. Petculescu, A. O. Mandru, William M. Yuhasz, Thomas A. Lograsso, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway Apr 2010

The Effect Of Partial Substitution Of Ge For Ga On The Elastic And Magnetoelastic Properties Of Fe–Ga Alloys, G. Petculescu, A. O. Mandru, William M. Yuhasz, Thomas A. Lograsso, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

Ames Laboratory Conference Papers, Posters, and Presentations

Both components of the tetragonal magnetoelastic constant b1: the saturation magnetostriction, λγ,2 = (3/2)λ100, and the magnetic-field saturated shear elasticity, c′ = (c11c12)/2, were investigated over a wide temperature range for the magnetostrictiveFe1−xyGaxGey alloys, (x+y ≅ 0.125, 0.185, and 0.245; x/y ≅ 1 and 3). The magnetostriction was measured from 77 to 425 K using standard strain gage techniques. Both shear elastic constants (c′ and c44) were measured from 5 to 300 K using resonant ultrasound spectroscopy. Six alloy compositions were ...


Magnetostrictive And Elastic Properties Of Fe100−Xmox (2, Mianliang Huang, A. O. Mandru, G. Petculescu, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso Apr 2010

Magnetostrictive And Elastic Properties Of Fe100−Xmox (2, Mianliang Huang, A. O. Mandru, G. Petculescu, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

In this paper we investigate the magnetostrictive [(3/2)λ100 and (3/2)λ111] and elastic (c′and c44) behavior of single crystalline alloys Fe100−xMox for 21 and −b2) are computed from the measurements. Similar to other Fe–X (X = Al, Ga, and Ge) alloys, the tetragonal magnetostriction (3/2)λ100 increases monotonically from ∼ 70×10−6 at ∼ 2.5 at. % Mo to a maximum of either ∼ 100×10−6 at ∼ 8 at. % Mo for the slow cooled crystals or ∼ 125×10−6 at ∼ 11 at. % Mo for quenched crystals. A ...


Magnetoelasticity Of Fe–Si Single Crystals, Qingfeng Xing, D. Wu, Thomas A. Lograsso Apr 2010

Magnetoelasticity Of Fe–Si Single Crystals, Qingfeng Xing, D. Wu, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

The tetragonal magnetostriction constant, (3/2)λ100, of Fe–Si single crystals was measured and was found to be structure dependent. Similar to that of Fe–Ge single crystals, (3/2)λ100 is positive in the single phase A2 regime, becomes negative in the single phase D03 regime, and changes from positive to negative between the two regimes. Short-range order in the A2 regime decreases the magnetostriction prior to the onset of long range order. In the single phase regions of both A2 and D03, thermal history does not show any obvious effect on the magnetostriction ...