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Iowa State University

2013

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Articles 1 - 30 of 64

Full-Text Articles in Physics

Azimuthal Anisotropy Of Pi(0) And Eta Mesons 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 Dec 2013

Azimuthal Anisotropy Of Pi(0) And Eta Mesons 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

The azimuthal anisotropy coefficients v2 and v4 of p 0 and. mesons are measured in Au + Au collisions at root s(NN) = 200 GeV as a function of transverse momentum p(T) (1-14 GeV/c) and centrality. The extracted v(2) coefficients are found to be consistent between the two meson species over the measured p(T) range. The ratio of v(4)/v(2)(2) for pi(0) mesons is found to be independent of p(T) for 1- 9 GeV/c, implying a lack of sensitivity of the ratio to the change of underlying physics with p(T ...


Quadrupole Anisotropy In Dihadron Azimuthal Correlations In Central D 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, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Nov 2013

Quadrupole Anisotropy In Dihadron Azimuthal Correlations In Central D 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, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in d + Au collisions at root s(NN) = 200 GeV. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central p + Pb collisions at root s(NN) = 5.02 TeV, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in d + Au collisions at RHIC compared to those seen ...


Nuclear Modification Of Psi ', Chi(C), And J/Psi Production In D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Nov 2013

Nuclear Modification Of Psi ', Chi(C), And J/Psi Production In D Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present results for three charmonia states (psi' chi(c), and J/ psi) in d + Au collisions at vertical bar y vertical bar < 0.35 and root s(NN) = 200 GeV. We find that the modification of the psi' yield relative to that of the J/ psi scales approximately with charged particle multiplicity at midrapidity across p + A, d + Au, and A + A results from the Super Proton Synchrotron and the Relativistic Heavy Ion Collider. In large-impact-parameter collisions we observe a similar suppression for the psi' and J/ psi, while in small-impact-parameter collisions the more weakly bound psi' is more strongly suppressed. Owing to the short time spent traversing the Au nucleus, the larger psi' suppression in central events is not explained by an increase of the nuclear absorption owing to meson formation time effects.


Electrical Resistivity Study Of Cezn11: Magnetic Field And Pressure Phase Diagram Up To 5 Gpa, Valentin Taufour, Halyna Hodovanets, Stella K. Kim, Sergey L. Bud'ko, Paul C. Canfield Nov 2013

Electrical Resistivity Study Of Cezn11: Magnetic Field And Pressure Phase Diagram Up To 5 Gpa, Valentin Taufour, Halyna Hodovanets, Stella K. Kim, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

Thorough resistivity measurements on single crystals of CeZn11 under pressure p and magnetic field H are presented. At ambient pressure, CeZn11 orders antiferromagnetically at TN=2 K. The pressure dependence of the resistivity reveals an increase of the Kondo effect. We determine the pressure evolution of the magnetic exchange interaction between conduction and localized 4f electrons. It qualitatively reproduces the pressure evolution of the magnetic ordering temperature TO1 (with TO1=TN at ambient pressure). In addition to TO1, a new anomaly TO2appears under pressure. Both anomalies are found to increase with applied pressure up to 4.9 GPa, indicating that ...


Magnetic Structures And Interplay Between Rare-Earth Ce And Fe Magnetism In Single-Crystal Cefeaso, Qiang Zhang, Wei Tan, Haifeng Li, Jong-Woo Kim, Jiaqiang Yan, R. William Mccallum, Thomas A. Lograsso, Jerel L. Zarestky, Sergey L. Bud’Ko, Robert J. Mcqueeney, David Vaknin Nov 2013

Magnetic Structures And Interplay Between Rare-Earth Ce And Fe Magnetism In Single-Crystal Cefeaso, Qiang Zhang, Wei Tan, Haifeng Li, Jong-Woo Kim, Jiaqiang Yan, R. William Mccallum, Thomas A. Lograsso, Jerel L. Zarestky, Sergey L. Bud’Ko, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Publications

Neutron and synchrotron resonant x-ray magnetic scattering (RXMS) complemented by heat capacity and resistivity measurements reveal the evolution of the magnetic structures of Fe and Ce sublattices in a CeFeAsO single crystal. The RXMS of magnetic reflections at the Ce L-II edge shows a magnetic transition that is specific to the Ce antiferromagnetic long-range ordering at T-Ce approximate to 4 K with short-range Ce ordering above T-Ce, whereas neutron diffraction measurements of a few magnetic reflections indicate a transition at T* approximate to 12 K with an unusual order parameter. Detailed order-parameter measurements on several magnetic reflections by neutrons show ...


Low-Energy Planar Magnetic Defects In Bafe2as2: Nanotwins, Twins, Antiphase, And Domain Boundaries, Suffian N. Khan, Aftab Alam, Duane D. Johnson Nov 2013

Low-Energy Planar Magnetic Defects In Bafe2as2: Nanotwins, Twins, Antiphase, And Domain Boundaries, Suffian N. Khan, Aftab Alam, Duane D. Johnson

Ames Laboratory Publications

In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study, using density-functional theory, the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated nanotwins (twin nuclei), and spin excitations proposed and/or observed. These nanoscale defects have a very low surface energy (22–210 m Jm−2), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries—making a uniform-moment picture inappropriate for long-range magnetic order in real samples. Nanotwins explain features in measured pair distribution functions so should ...


Suppression Of Ferromagnetism In The Lavxcr1−Xge3 System, Xiao Lin, Valentin Taufour, Sergey L. Bud'ko, Paul C. Canfield Sep 2013

Suppression Of Ferromagnetism In The Lavxcr1−Xge3 System, Xiao Lin, Valentin Taufour, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

We report the synthesis of hexagonal LaVxCr1−xGe3 (x=0–0.21, 1.00) single crystals and present a systematic study of this series by measurements of temperature- and field-dependent magnetic susceptibility, magnetization, resistivity, and specific heat. Ferromagnetism has been observed for x=0–0.21. The Curie temperature declines monotonically as the V concentration increases. Single-crystalline samples could only be grown for x values up to 0.21 for which the transition temperature was suppressed down to 36 K. Although we could not fully suppress TC via V substitution, for x=0.16, we performed magnetization measurements under pressure ...


Quantitative Vibrational Dynamics Of The Metal Site In A Tin Porphyrin: An Ir, Nrvs, And Dft Study, Bogdan M. Leu, Marek Z. Zgierski, Christian Michael Bischoff, Ming Li, Michael Y. Hu, Jiyoung Zhao, Steve W. Martin, Esen Ercan Alp, W. Robert Scheidt Sep 2013

Quantitative Vibrational Dynamics Of The Metal Site In A Tin Porphyrin: An Ir, Nrvs, And Dft Study, Bogdan M. Leu, Marek Z. Zgierski, Christian Michael Bischoff, Ming Li, Michael Y. Hu, Jiyoung Zhao, Steve W. Martin, Esen Ercan Alp, W. Robert Scheidt

Materials Science and Engineering Publications

We used a newer, synchrotron-based, spectroscopic technique (nuclear resonance vibrational spectroscopy, NRVS) in combination with a more traditional one (infrared absorption, IR) to obtain a complete, quantitative picture of the metal center vibrational dynamics in a six-coordinated tin porphyrin. From the NRVS 119Sn site-selectivity and the sensitivity of the IR signal to 112Sn/119Sn isotope substitution, we identified the frequency of the antisymmetric stretching of the axial bonds (290 cm–1) and all the other vibrations involving Sn. Experimentally authenticated density functional theory (DFT) calculations aid the data interpretation by providing detailed normal mode descriptions for each observed vibration. These ...


Thermal Expansion Of Cafe2as2: Effect Of Cobalt Doping And Postgrowth Thermal Treatment, Sergey L. Bud'ko, Sheng Ran, Paul C. Canfield Aug 2013

Thermal Expansion Of Cafe2as2: Effect Of Cobalt Doping And Postgrowth Thermal Treatment, Sergey L. Bud'ko, Sheng Ran, Paul C. Canfield

Ames Laboratory Publications

We report thermal expansion measurements on Ca(Fe1−xCox)2As2 single crystals with different thermal treatment, with samples chosen to represent four different ground states observed in this family. For all samples, thermal expansion is anisotropic with different signs of the in-plane and c-axis thermal expansion coefficients in the high temperature, tetragonal phase. The features in thermal expansion associated with the phase transitions are of opposite signs as well, pointing to a different response of transition temperatures to the in-plane and the c-axis stress. These features, and consequently the inferred pressure derivatives, are very large, clearly and substantially exceeding those ...


Spectra And Ratios Of Identified Particles In Au Plus Au And D Plus Au Collisions At Root S(Nn)=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 Aug 2013

Spectra And Ratios Of Identified Particles In Au Plus Au And D Plus Au Collisions At Root S(Nn)=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

The transverse momentum (p(T)) spectra and ratios of identified charged hadrons (pi(+/-), K-+/-, p, (p) over bar) produced in root s(NN) = 200 GeV Au + Au and d + Au collisions are reported in five different centrality classes for each collision species. The measurements of pions and protons are reported up to p(T) = 6 GeV/c (5 GeV/c), and the measurements of kaons are reported up to p(T) = 4 GeV/c (3.5 GeV/c) in Au + Au (d + Au) collisions. In the intermediate p(T) region, between 2 and 5 GeV/c, a significant enhancement of ...


Inclusive Cross Section And Single Transverse Spin Asymmetry For Very Forward Neutron Production In Polarized 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 Aug 2013

Inclusive Cross Section And Single Transverse Spin Asymmetry For Very Forward Neutron Production In Polarized 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

The energy dependence of the single-transverse-spin asymmetry, A(N), and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at the Relativistic Heavy Ion Collider for polarized p + p collisions at root s = 200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with a momentum fraction of x(F) = 0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x(F) scaling, compared to measurements by an experiment at the Intersecting Storage ...


Modeling Interacting Dynamic Networks: I. Preferred Degree Networks And Their Characteristics, Wenjia Liu, Shivakumar Jolad, Beate Schmittmann, R. K. P. Zia Aug 2013

Modeling Interacting Dynamic Networks: I. Preferred Degree Networks And Their Characteristics, Wenjia Liu, Shivakumar Jolad, Beate Schmittmann, R. K. P. Zia

Physics and Astronomy Publications

We study a simple model of dynamic networks, characterized by a set preferred degree, κ. Each node with degree k attempts to maintain its κ and will add (cut) a link with probability w(k;κ) (1 − w(k;κ)). As a starting point, we consider a homogeneous population, where each node has the same κ, and examine several forms of w(k;κ), inspired by Fermi–Dirac functions. Using Monte Carlo simulations, we find the degree distribution in the steady state. In contrast to the well known Erdős–Rényi network, our degree distribution is not a Poisson distribution; yet ...


Medium Modification Of Jet Fragmentation In Au Plus Au Collisions At Root S-Nn=200 Gev Measured In Direct Photon-Hadron Correlations, Andrew Adare, Lei Ding, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, S. Skutnik, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Jul 2013

Medium Modification Of Jet Fragmentation In Au Plus Au Collisions At Root S-Nn=200 Gev Measured In Direct Photon-Hadron Correlations, Andrew Adare, Lei Ding, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, S. Skutnik, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The jet fragmentation function is measured with direct photon-hadron correlations in p + p and Au + Au collisions at root S-NN = 200 GeV. The P-T of the photon is an excellent approximation to the initial P-T of the jet and the ratio Z(T) = P-T(h)/P-T(gamma) is used as a proxy for the jet fragmentation function. A statistical subtraction is used to extract the direct photon-hadron yields in Au + Au collisions while a photon isolation cut is applied in p + p. I-AA, the ratio of hadron yield opposite the photon in Au + Au to that in p + p, indicates ...


Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant Jul 2013

Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant

Iowa State University Patents

A multi-channel polarized thermal emitter (PTE) is presented. The multi-channelPTE can emit polarized thermal radiation without using a polarizer at normal emergence. The multi-channel PTE consists of two layers of metallic gratings on a monolithic and homogeneous metallic plate. It can be fabricated by a low-cost soft lithography technique called two-polymer microtransfer molding. The spectral positions of the mid-infrared (MIR) radiation peaks can be tuned by changing the periodicity of the gratings and the spectral separation between peaks are tuned by changing the mutual angle between the orientations of the two gratings.


Characterizing Acoustic Fluidized Bed Hydrodynamics Using X-Ray Computed Tomography, David R. Escudero, Theodore J. Heindel Jul 2013

Characterizing Acoustic Fluidized Bed Hydrodynamics Using X-Ray Computed Tomography, David R. Escudero, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Fluidized bed reactors are important assets of many industrial applications because they provide uniform temperature distributions, low pressure drops, and high heat/mass rates. Characterizing the hydrodynamics of a fluidized bed is important to better understand the behavior of these multiphase flow systems. The hydrodynamic behavior in a cold flow 3D fluidized bed, with and without acoustic intervention, using X-ray computed tomography is investigated in this study. Experiments are carried out in a 10.2 cm ID fluidized bed filled with glass beads, with material density of 2600 kg/m3 and particle size ranges between 212–600 μm. In ...


A High-Speed X-Ray Detector System For Noninvasive Fluid Flow Measurements, Timothy B. Morgan, Benjamin R. Halls, Terrence R. Meyer, Theodore J. Heindel Jul 2013

A High-Speed X-Ray Detector System For Noninvasive Fluid Flow Measurements, Timothy B. Morgan, Benjamin R. Halls, Terrence R. Meyer, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

The opaque nature of many multiphase flows has long posed a significant challenge to the visualization and measurement of desired characteristics. To overcome this difficulty, X-ray imaging, both in the form of radiography and computed tomography, has been used successfully to quantify various multiphase flow phenomena. However, the relatively low temporal resolution of typical X-ray systems limit their use to moderately slow flows and time-average values. This paper discusses the development of an X-ray detection system capable of high-speed radiographic imaging that can be used to visualize multiphase flows. Details of the hardware will be given and then applied to ...


Chip Segmentation In Machining: A Study Of Deformation Localization Characteristics In Ti6al4v, Abhijit Chandra, Pavan Karra, Adam Bragg, Jie Wang, Gap-Yong Kim Jun 2013

Chip Segmentation In Machining: A Study Of Deformation Localization Characteristics In Ti6al4v, Abhijit Chandra, Pavan Karra, Adam Bragg, Jie Wang, Gap-Yong Kim

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Chip segmentation by deformation localization is an important process in a certain range of velocities and might be desirable in reducing cutting forces and by improving chips’ evacuation, whereas few studies of practical criteria to calculate shear band spacing are available in literature. This paper extends nonlinear dynamics model for chip segmentation by allowing time varying orientation of the shear plane that are pronounced in strain hardening materials. The model extends the non-linear dynamics approach with additional state variables to the Burns and Davies approach. The model is simulated numerically to predict the shear bands of the chip. The numerical ...


Low Resistivity Contact To Iron-Pnictide Superconductors, Makariy A. Tanatar, Ruslan Prozorov, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield May 2013

Low Resistivity Contact To Iron-Pnictide Superconductors, Makariy A. Tanatar, Ruslan Prozorov, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield

Iowa State University Patents

Method of making a low resistivity electrical connection between an electrical conductor and an iron pnictide superconductor involves connecting the electrical conductor and superconductor using a tin or tin-based material therebetween, such as using a tin or tin-based solder. The superconductor can be based on doped AFe2As2, where A can be Ca, Sr, Ba, Eu or combinations thereof for purposes of illustration only.


Direct Photon Production In D+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration May 2013

Direct Photon Production In D+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Direct photons have been measured in root s(NN) = 200 GeV d + Au collisions at midrapidity. A wide p(T) range is covered by measurements of nearly real virtual photons (1 < p(T) < 6 GeV/c) and real photons (5 < p(T) < 16 GeV/c). The invariant yield of the direct photons in d + Au collisions over the scaled p + p cross section is consistent with unity. Theoretical calculations assuming standard cold-nuclear-matter effects describe the data well for the entire p(T) range. This indicates that the large enhancement of direct photons observed in Au + Au collisions for 1.0 < p(T) < 2.5 GeV/c is attributable to a source other than the initial-state nuclear effects.


Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso May 2013

Texture And Grain Morphology Dependencies Of Saturation Magnetostriction In Rolled Polycrystalline Fe83ga17, R. A. Kellogg, A. B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

Textured polycrystalline Fe-Ga alloys exhibit magnetostrictive strains of 100 ppm or greater and may function as a mechanically robust actuator/sensing material. Current efforts seek to combine the 300+ ppm magnetostrictive strain performance of [100] oriented single crystals with the mechanical properties of polycrystalline forms. One approach to combining these properties is to control the crystallographic texture through deformation processing such as rolling. To determine the relationship between saturation magnetostriction, degree of texturing, and grain morphology we compare the results of three-dimensional finite element simulations with the analytical solution for a random polycrystal and the experimental responses of rolled polycrystalline ...


Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney Apr 2013

Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering measurements demonstrate that the magnetic interactions in antiferromagnetic LaFeAsO are two dimensional. Spin-wave velocities within the Fe layer and the magnitude of the spin gap are similar to the AFe2As2 based materials. However, the ratio of interlayer and intralayer exchange is found to be less than ∼10−4 in LaFeAsO, very similar to the cuprates, and ∼100 times smaller than that found in AFe2As2 compounds. The results suggest that the effective dimensionality of the magnetic system is highly variable in the parent compounds of the iron arsenides and weak three-dimensional interactions ...


Gamma (1s+2s+3s) Production In D Plus Au And P Plus P Collisions At Root S(Nn)=200 Gev And Cold-Nuclear-Matter Effects, 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 Apr 2013

Gamma (1s+2s+3s) Production In D Plus Au And P Plus P Collisions At Root S(Nn)=200 Gev And Cold-Nuclear-Matter Effects, 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

The three gamma states, gamma (1S + 2S + 3S), are measured in d + Au and p + p collisions at root s(NN) = 200 GeV and rapidities 1.2 < vertical bar y vertical bar < 2.2 by the PHENIX experiment at the Relativistic Heavy Ion Collider. Cross sections for the inclusive gamma (1S + 2S + 3S) production are obtained. The inclusive yields per binary collision for d + Au collisions relative to those in p + p collisions (R-dAu) are found to be 0.62 +/- 0.26 (stat) +/- 0.13 (syst) in the gold-going direction and 0.91 +/- 0.33 (stat) +/- 0.16 (syst) in the deuteron-going direction. The measured results are compared to a nuclear-shadowing model, EPS09 [Eskola et al., J. High Energy Phys. 04 (2009) 065], combined with a final-state breakup cross section, sigma(br), and compared to lower energy p + A results. We also compare the results to the PHENIX J/psi results [Adare et al., Phys. Rev. Lett. 107, 142301 (2011)]. The rapidity dependence of the observed gamma suppression is consistent with lower energy p + A measurements.


Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov Apr 2013

Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Publications

Measurements of temperature-dependent in-plane resistivity ρ(T) were used to determine the upper critical field and its anisotropy in high-quality single crystals of the stoichiometric iron arsenide superconductor KFe2As2. The crystals were characterized by the residual resistivity ratio ρ(300 K)/ρ(0) up to 3000 and the resistive transition midpoint temperature Tc=3.8 K, significantly higher than in previous studies on the same material. We find increased Hc2(T) for both directions of the magnetic field, which scale with the increased Tc. This unusual linear Hc2(Tc) scaling is not ...


Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Apr 2013

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Conference Papers, Posters, and Presentations

The phonon dispersion was measured at room temperature (above the Néel temperature TN) along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Magnetostructural effects are well documented in the AFe2As2-based (A = Ca, Sr, Ba, Eu) systems. Only recently have single crystals of LaFeAsO become available. The experimentally observed splitting between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 materials are confirmed to be present in LaFeAsO. This is discussed ...


Neutral Pion Production With Respect To Centrality And Reaction Plane 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 Mar 2013

Neutral Pion Production With Respect To Centrality And Reaction Plane 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

The PHENIX experiment has measured the production of pi(0)s in Au + Au collisions at root S-NN = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p(T), to 20 GeV/c. The production ratio of eta/pi(0) is 0.46 +/- 0.01(stat) +/- 0.05(syst), constant with p(T) and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p + p and d + Au values. pi(0) are suppressed by a factor of 5, as in earlier ...


Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Mar 2013

Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Publications

The phonon dispersion was measured at room temperature along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Spin-polarized first-principles calculations imposing various types of antiferromagnetic order are in better agreement with the experimental results than nonmagnetic calculations, although the measurements were made well above the magnetic ordering temperature, TN. Splitting observed between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 (A=Ca,Sr,Ba,Eu) materials are present in LaFeAsO. The inclusion of Fe ...


Magnetoelastic Coupling And Charge Correlation Lengths In A Twin Domain Of Ba(Fe1−Xcox)2as2 (X=0.047): A High-Resolution X-Ray Diffraction Study, Qiang Zhang, Wenjie Wang, Jong-Woo Kim, Benjamin Hansen, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield, Robert J. Mcqueeney, David Vaknin Mar 2013

Magnetoelastic Coupling And Charge Correlation Lengths In A Twin Domain Of Ba(Fe1−Xcox)2as2 (X=0.047): A High-Resolution X-Ray Diffraction Study, Qiang Zhang, Wenjie Wang, Jong-Woo Kim, Benjamin Hansen, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Publications

The interplay between structure, magnetism, and superconductivity in single crystal Ba(Fe1−xCox)2As2 (x=0.047) has been studied using high-resolution x-ray diffraction by monitoring charge Bragg reflections in each twin domain separately. The emergence of the superconducting state is correlated with the suppression of the orthorhombic distortion around TC, exhibiting competition between orthorhombicity and superconductivity. Above TS, the in-plane charge correlation length increases with the decrease of temperature, possibly induced by nematic fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in the in-plane charge correlation lengths along a (ξa) and baxes (ξb) are observed at TS and ...


Transverse-Momentum Dependence Of The J/Psi Nuclear Modification In D+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Mar 2013

Transverse-Momentum Dependence Of The J/Psi Nuclear Modification In D+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present measured J/psi production rates in d + Au collisions at root s(NN) = 200 GeV over broad ranges of transverse momentum (p(T) = 0-14 GeV/c) and rapidity (-2.2 < y < 2.2). We construct the nuclear-modification factor R-dAu for these kinematics and as a function of collision centrality (related to impact parameter for the d + Au collision). We find that the modification is largest for collisions with small impact parameters and observe a suppression (R-dAu < 1) for p(T) < 4 GeV/c at positive rapidities. At negative rapidity we observe a suppression for p(T) < 2 GeV/c then an enhancement (R-dAu > 1) for p(T) > 2 GeV/c. The observed enhancement at negative rapidity has implications for the interpretation of the observed modification in heavy-ion collisions at high p(T).


Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson Mar 2013

Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson

Ames Laboratory Publications

Formation energies of native defects in Bi2(TexSe3−x), with comparison to ideal Bi2Te2S, are calculated in density-functional theory to assess transport properties. Bi2Se3 is found to be n type for both Bi- and Se-rich growth conditions, while Bi2Te3 changes fromn to p type going from Te- to Bi-rich conditions, as observed. Bi2Te2Se and Bi2Te2S are generally n type, explaining observed heavily doped n-type behavior in most samples. A (0/−) transition level at 16 meV above valence-band maximum ...


Stability Maps To Predict Anomalous Ductility In B2 Materials, Ruoshi Sun, Duane D. Johnson Mar 2013

Stability Maps To Predict Anomalous Ductility In B2 Materials, Ruoshi Sun, Duane D. Johnson

Ames Laboratory Publications

While most B2 materials are brittle, a new class of B2 (rare-earth) intermetallic compounds is observed to have large ductility. We analytically derive a necessary condition for ductility (dislocation motion) involving ⟨111⟩ versus ⟨001⟩ slip and the relative stability of various planar defects that must form. We present a sufficient condition for antiphase boundary bistability on {11¯0} and {112¯} planes that allows multiple slip systems. From these energy-based criteria, we construct two stability maps for B2 ductility that use only dimensionless ratios of elastic constants and defect energies, calculated via density functional theory. These two conditions fully explain and ...