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Iowa State University

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2014

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Articles 1 - 30 of 69

Full-Text Articles in Physics

Shape-Memory Transformations Of Niti: Minimum-Energy Pathways Between Austenite, Martensites, And Kinetically Limited Intermediate States, Nikolai A. Zarkevich, Duane D. Johnson Dec 2014

Shape-Memory Transformations Of Niti: Minimum-Energy Pathways Between Austenite, Martensites, And Kinetically Limited Intermediate States, Nikolai A. Zarkevich, Duane D. Johnson

Ames Laboratory Publications

NiTi is the most used shape-memory alloy; nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudged elastic band method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between a body-centered orthorhombic (bco) ground state and a newly identified stable austenite (“glassy” B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited Rphase), and between martensite variants (bco orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed ...


Nuclear Matter Effects On J/Psi Production In Asymmetric Cu Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Nicole J. Apadula, Sarah C. Campbell, Lei Ding, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, Joshua Perry, Marzia Rosati, Alex Shaver, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration Dec 2014

Nuclear Matter Effects On J/Psi Production In Asymmetric Cu Plus Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Nicole J. Apadula, Sarah C. Campbell, Lei Ding, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, Joshua Perry, Marzia Rosati, Alex Shaver, M. Shimomura, Arbin Timilsina, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report on J/psi production from asymmetric Cu + Au heavy-ion collisions at root S-NN = 200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of J/psi yields in Cu + Au collisions in the Au-going direction is found to be comparable to that in Au + Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, J/psi production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due ...


Thermophonon, Nikolai A. Zarkevich Dec 2014

Thermophonon, Nikolai A. Zarkevich

Ames Laboratory Software

ThermoPhonon is a stand-alone code, which can be integrated into other software packages. Typically, it is used together with a density functional theory (DFT) code (such as VASP, Wien2k, AbInit, SIESTA) and a phonon code (such as Phonopy or Phon). The workflow is the following.

  • Molecular dynamics (MD) in a supercell at a given temperature T is performed using another code. After sufficient equilibration, the output in the form of atomic positions and forces for a large number of selected MD steps is recorded into a file. If needed, one can modify this file by applying additional constraints, such as ...


Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso Dec 2014

Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso

Ames Laboratory Publications

We report on the doping evolution of magnetic susceptibility χ(T) and Hall coefficient RH in high-quality Ba1−xKxFe2As2 (0.13≤x≤1) single crystals. It is found that the normal-state magnetic susceptibility of Ba1−xKxFe2As2 compounds undergoes a crossover from linear-T dependence in the undoped and underdoped samples into KFe2As2-type magnetic response in the overdoped samples with increasing K content. Although magnetic susceptibility χ(T) of optimally doped samples (0.34≤x≤0.47) still follows a monotonic increase with increasing temperature, a big hump around 300 K emerges. As x exceeds 0.53, a broad peak forms in ...


Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides Dec 2014

Nonclassical “Explosive” Nucleation In Pb/Si(111) At Low Temperatures, Matthew T. Hershberger, Myron Hupalo, Patricia A. Thiel, Cai-Zhuang Wang, Kai-Ming Ho, Michael C. Tringides

Chemistry Publications

Classically, the onset of nucleation is defined in terms of a critical cluster of the condensed phase, which forms from the gradual aggregation of randomly diffusing adatoms. Experiments in Pb/Si(111) at low temperature have discovered a dramatically different type of nucleation, with perfect crystalline islands emerging “explosively” out of the compressed wetting layer after a critical coverage Θc ¼ 1.22 ML is reached. The unexpectedly high island growth rates, the directional correlations in the growth of neighboring islands and the persistence in time of where mass is added in individual islands, suggest that nucleation is a result ...


Composition-Dependent Stability Of The Medium-Range Order Responsible For Metallic Glass Formation, Feng Zhang, Min Ji, Xiao-Wei Fang, Yang Sun, Cai-Zhuang Wang, Mikhail I. Mendelev, Matthew J. Kramer, Ralph E. Napolitano, Kai-Ming Ho Dec 2014

Composition-Dependent Stability Of The Medium-Range Order Responsible For Metallic Glass Formation, Feng Zhang, Min Ji, Xiao-Wei Fang, Yang Sun, Cai-Zhuang Wang, Mikhail I. Mendelev, Matthew J. Kramer, Ralph E. Napolitano, Kai-Ming Ho

Materials Science and Engineering Publications

The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. We focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. Our results show that a Bergman-type motif ...


Configurational Thermodynamics Of Alloyed Nanoparticles With Adsorbates, Lin-Lin Wang, Teck L. Tan, Duane D. Johnson Nov 2014

Configurational Thermodynamics Of Alloyed Nanoparticles With Adsorbates, Lin-Lin Wang, Teck L. Tan, Duane D. Johnson

Ames Laboratory Publications

Changes in the chemical configuration of alloyed nanoparticle (NP) catalysts induced by adsorbates under working conditions, such as reversal in core–shell preference, are crucial to understand and design NP functionality. We extend the cluster expansion method to predict the configurational thermodynamics of alloyed NPs with adsorbates based on density functional theory data. Exemplified with PdRh NPs having O-coverage up to a monolayer, we fully detail the core–shell behavior across the entire range of NP composition and O-coverage with quantitative agreement to in situ experimental data. Optimally fitted cluster interactions in the heterogeneous system are the key to enable ...


Green's Function Multiple-Scattering Theory With A Truncated Basis Set: An Augmented-Kkr Formalism, Aftab Alam, Suffian N. Khan, Andrei V. Smirnov, D. M. Nicholson, Duane D. Johnson Nov 2014

Green's Function Multiple-Scattering Theory With A Truncated Basis Set: An Augmented-Kkr Formalism, Aftab Alam, Suffian N. Khan, Andrei V. Smirnov, D. M. Nicholson, Duane D. Johnson

Ames Laboratory Publications

The Korringa-Kohn-Rostoker (KKR) Green's function, multiple-scattering theory is an efficient site-centered, electronic-structure technique for addressing an assembly of N scatterers. Wave functions are expanded in a spherical-wave basis on each scattering center and indexed up to a maximum orbital and azimuthal number Lmax=(l,m)max, while scattering matrices, which determine spectral properties, are truncated at Ltr=(l,m)tr where phase shifts δl>ltr are negligible. Historically, Lmax is set equal to Ltr, which is correct for large enough Lmax but not computationally expedient; a better procedure retains higher-order (free-electron and single-site) contributions for Lmax>Ltr with δl ...


Comparative Study Of Magnetic Properties Of Nanoparticles By High-Frequency Heat Dissipation And Conventional Magnetometry, V. Malik, J. Goodwill, Surya K. Mallapragada, Tanya Prozorov, Ruslan Prozorov Nov 2014

Comparative Study Of Magnetic Properties Of Nanoparticles By High-Frequency Heat Dissipation And Conventional Magnetometry, V. Malik, J. Goodwill, Surya K. Mallapragada, Tanya Prozorov, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

The rate of heating of 15 nm uniformly-sized magnetic aqueous nanoparticles suspension by high-amplitude and high-frequency ac magnetic field induced by the resonating LC circuit was measured. The results are analyzed in terms of specific energy absorption rate (SAR). Fitting field amplitude and frequency dependences of SAR to the linear response theory, magnetic moment per particles was extracted. The value of magnetic moment was independently evaluated from dc magnetization measurements of a frozen colloid by fitting field-dependent magnetization to a Langevin function. The two methods produced similar results, which are compared to the theoretical expectation for this particle size. Additionally ...


Measurement Of K-S(0) And K*(0) In P Plus P, D Plus Au, And Cu Plus Cu Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole J. Apadula, Saraj C. Campbell, Lei Ding, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, S. Skutnik, Arbin Timilsina, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Nov 2014

Measurement Of K-S(0) And K*(0) In P Plus P, D Plus Au, And Cu Plus Cu Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole J. Apadula, Saraj C. Campbell, Lei Ding, Alan Dion, Nathan C. Grau, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, S. Skutnik, Arbin Timilsina, Carla Vale, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a systematic study of K-S(0) and K*(0) meson production at midrapidity in p + p, d + Au, and Cu + Cu collisions at root s(NN) = 200 GeV. The K-S(0) and K*(0) mesons are reconstructed via their K-S(0) -> pi(0)(-> gamma gamma) pi(0)(-> gamma gamma) and K*(0) -> K-+/-pi(-/+) decay modes, respectively. The measured transverse-momentum spectra are used to determine the nuclear modification factor of K-S(0) and K*(0) mesons in d + Au and Cu + Cu collisions at different centralities. In the d ...


Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel Nov 2014

Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel

Chemistry Publications

We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.


Cross Section And Transverse Single-Spin Asymmetry Of Eta Mesons In P Up Arrow Plus P Collisions At Root S=200 Gev At Forward Rapidity, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Fang Wei, Shawn Whitaker, Et Al., Phenix Collaboration Oct 2014

Cross Section And Transverse Single-Spin Asymmetry Of Eta Mesons In P Up Arrow Plus P Collisions At Root S=200 Gev At Forward Rapidity, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Fang Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present a measurement of the cross section and transverse single-spin asymmetry (AN) for. mesons at large pseudorapidity from root s = 200 GeV p up arrow + p collisions. The measured cross section for 0.5 < p(T) < 5.0 GeV/c and 3.0 < vertical bar eta vertical bar < 3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries A(N) have been measured as a function of Feynman-x (x(F)) from 0.2 < vertical bar x(F)vertical bar < 0.7, as well as transverse momentum (p(T)) from 1.0 < p(T) < 4.5 GeV/c. The asymmetry averaged over positive x(F) is < A(N)> = 0.061 +/- 0.014. The results are consistent with prior transverse single-spin measurements of forward eta and pi(0) mesons at various energies in overlapping x(F) ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p up arrow + p collisions.


Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman Oct 2014

Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman

Ames Laboratory Publications

Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At TN≈7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector (0 0 τ) with τ≈14 and the magnetic moment along the a axis of the orthorhombic unit cell. Below TLI≈5 K, the magnetic structure locks in to a commensurate structure with τ=14 and the magnetic moment remains along the a axis. Below T☆≈4 K, we find additional half-integer and integer ...


Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld Oct 2014

Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld

Ames Laboratory Publications

A single crystal of isovalently substituted Ba(Fe1−xRux)2As2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×1019 e−/cm2. The electrical resistivity is measuredin situ at T=22  K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tccompared to other types of artificially introduced disorder, probably due to the strong short-range potential of the ...


Influence Of Composition And Heat Treatment On Damping And Magnetostrictive Properties Of Fe–18%(Ga + Al) Alloys, I. S. Golovin, V. V. Palacheva, V. Yu. Zadorozhnyy, J. Zhu, H. Jiang, J. Cifre, Thomas A. Lograsso Oct 2014

Influence Of Composition And Heat Treatment On Damping And Magnetostrictive Properties Of Fe–18%(Ga + Al) Alloys, I. S. Golovin, V. V. Palacheva, V. Yu. Zadorozhnyy, J. Zhu, H. Jiang, J. Cifre, Thomas A. Lograsso

Ames Laboratory Publications

The structure, magnetostriction and damping properties of Fe82Ga(18−x)Alx (x = 0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe–18(Ga + Al) alloys was studied as a function of temperature (from 0 to 600 °C), frequency (from 0.01 to 200 Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of Fe–Ga–Al alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe–18% Ga alloys was found to ...


Unoccupied Electronic States Of Icosahedral Al-Pd-Mn Quasicrystals: Evidence Of Image Potential Resonance And Pseudogap, M. Maniraj, Abhishek Rai, S. R. Barman, M. Krajčí, Deborah L. Schlagel, Thomas A. Lograsso, K. Horn Sep 2014

Unoccupied Electronic States Of Icosahedral Al-Pd-Mn Quasicrystals: Evidence Of Image Potential Resonance And Pseudogap, M. Maniraj, Abhishek Rai, S. R. Barman, M. Krajčí, Deborah L. Schlagel, Thomas A. Lograsso, K. Horn

Ames Laboratory Publications

We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i−Al−Pd−Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function ...


Low-Mass Vector-Meson Production At Forward Rapidity In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration Sep 2014

Low-Mass Vector-Meson Production At Forward Rapidity In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Nicole Apadula, Sarah C. Campbell, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Milap R. Patel, H. Pei, Joshua Perry, Marzia Rosati, M. Shimomura, C. L. Silva, Arbin Timilsina, Feng Wei, Shawn Whitaker, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson, omega, rho, and phi, production through the dimuon decay channel at forward rapidity (1.2 < vertical bar y vertical bar < 2.2) in p + p collisions at root s = 200 GeV. The differential cross sections for these mesons are measured as a function of both p(T) and rapidity. We also report the integrated differential cross sections over 1 < p(T) < 7 GeV/c and 1.2 < vertical bar y vertical bar < 2.2: d sigma/dy(omega + rho rho -> mu mu) = 80 +/- 6(stat) +/- 12(syst)nb and d sigma/dy(phi -> mu mu) = 27 +/- 3(stat) +/- 4(syst)nb. These results are compared with midrapidity measurements and calculations.


System-Size Dependence Of Open-Heavy-Flavor Production In Nucleus-Nucleus Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, 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 2014

System-Size Dependence Of Open-Heavy-Flavor Production In Nucleus-Nucleus Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nicole Apadula, 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

The PHENIX Collaboration at the Relativistic Heavy Ion Collider has measured open-heavy-flavor production in Cu + Cu collisions at v root s(NN) = 200 GeV through the measurement of electrons at midrapidity that originate from semileptonic decays of charm and bottom hadrons. In peripheral Cu + Cu collisions an enhanced production of electrons is observed relative to p + p collisions scaled by the number of binary collisions. In the transverse momentum range from 1 to 5 GeV/c the nuclear modification factor is R-AA similar to 1.4. As the system size increases to more central Cu + Cu collisions, the enhancement gradually ...


Centrality Categorization Rp(D)+A In High-Energy Collisions, Andrew Adare, Nicole Apadula, 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 Sep 2014

Centrality Categorization Rp(D)+A In High-Energy Collisions, Andrew Adare, Nicole Apadula, 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

High-energy proton- and deuteron-nucleus collisions provide an excellent tool for studying a wide array of physics effects, including modifications of parton distribution functions in nuclei, gluon saturation, and color neutralization and hadronization in a nuclear environment, among others. All of these effects are expected to have a significant dependence on the size of the nuclear target and the impact parameter of the collision, also known as the collision centrality. In this article, we detail a method for determining centrality classes in p(d) + A collisions via cuts on the multiplicity at backward rapidity (i.e., the nucleus-going direction) and for ...


Raman Studies Of Nearly Half-Metallic Ferromagnetic Cos2, S. G. Lyapin, A. N. Utyuzh, A. E. Petrova, A. P. Novikov, Thomas A. Lograsso, S. M. Stishov Sep 2014

Raman Studies Of Nearly Half-Metallic Ferromagnetic Cos2, S. G. Lyapin, A. N. Utyuzh, A. E. Petrova, A. P. Novikov, Thomas A. Lograsso, S. M. Stishov

Ames Laboratory Publications

We measured the Raman spectra of ferromagnetic, nearly half-metallic, CoS2over a broad temperature range. All five Raman active modes Ag, Eg, Tg(1), Tg(2) and Tg(3) were observed. The magnetic ordering is indicated by a change of the temperature dependences of the frequency and the line width of Ag and Tg(2) modes at the Curie point. The temperature dependence of the frequencies and line widths of the Ag, Eg, Tg(1), Tg(2) modes in the paramagnetic phase can be described in the framework of the ...


Stable Atomic Structure Of Niti Austenite, Nikolai A. Zarkevich, Duane D. Johnson Aug 2014

Stable Atomic Structure Of Niti Austenite, Nikolai A. Zarkevich, Duane D. Johnson

Ames Laboratory Publications

Nitinol (NiTi), the most widely used shape-memory alloy, exhibits an austenite phase that has yet to be identified. The usually assumed austenitic structure is cubic B2, which has imaginary phonon modes, hence it is unstable. We suggest a stable austenitic structure that “on average” has B2 symmetry (observed by x-ray and neutron diffraction), but it exhibitsfinite atomic displacements from the ideal B2 sites. The proposed structure has a phonon spectrum that agrees with that from neutron scattering, has diffraction spectra in agreement with x-ray diffraction, and has an energy relative to the ground state that agrees with calorimetry data.


Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield Aug 2014

Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield

Ames Laboratory Publications

We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1−xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as ...


High-Speed 3d Shape Measurement With Fiber Interference, Beiwen Li, Pan Ou, Song Zhang Aug 2014

High-Speed 3d Shape Measurement With Fiber Interference, Beiwen Li, Pan Ou, Song Zhang

Mechanical Engineering Conference Presentations, Papers, and Proceedings

This paper presents a miniaturized fringe projection system that only uses two fibers to potentially achieve superfast (e.g., MHz to GHz) 3D shape measurement speeds. The proposed method uses two optical fibers that carry the same wavelength of laser light with polarization and phase information properly modulated to generate high-quality sinusoidal fringe patterns through interference. The high-speed phase shifting is achieved by employing a high-speed Lithium Niobate (LN) electrooptic phase modulator. Since only two optical fibers are used to generate sinusoidal patterns, the system has a great potential of miniaturization for applications where the sensor size is critical (e ...


Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield Jul 2014

Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

We present a detailed characterization of the recently discovered i-R-Cd (R=Y,Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R ...


Inclusive Double-Helicity Asymmetries In Neutral-Pion And Eta-Meson Production In <(P) Over Right Arrow> + <(P) Over Right Arrow> 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, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Jul 2014

Inclusive Double-Helicity Asymmetries In Neutral-Pion And Eta-Meson Production In + 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, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, A(LL), for pi(0) and eta production in root s = 200 GeV polarized p + p collisions. Comparison of the pi(0) results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, Delta G, in the proton in the probed Bjorken x range. The effect of adding the new 2009 pi(0) data to a recent global analysis of polarized scattering data is also shown ...


Measurement Of Transverse-Single-Spin Asymmetries For Midrapidity And Forward-Rapidity Production Of Hadrons In Polarized P Plus P Collisions At Root S=200 And 62.4 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 Jul 2014

Measurement Of Transverse-Single-Spin Asymmetries For Midrapidity And Forward-Rapidity Production Of Hadrons In Polarized P Plus P Collisions At Root S=200 And 62.4 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

Measurements of transverse-single-spin asymmetries (A(N)) in p + p collisions at root s = 62.4 and 200 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider are presented. At midrapidity, A(N) is measured for neutral pion and eta mesons reconstructed from diphoton decay, and, at forward rapidities, neutral pions are measured using both diphotons and electromagnetic clusters. The neutral-pion measurement of A(N) at midrapidity is consistent with zero with uncertainties a factor of 20 smaller than previous publications, which will lead to improved constraints on the gluon Sivers function. At higher rapidities, where the valence quark ...


Langevin And Fokker-Planck Analyses Of Inhibited Molecular Passing Processes Controlling Transport And Reactivity In Nanoporous Materials, Chi-Jen Wang, David Ackerman, Igor I. Slowing, James W. Evans Jul 2014

Langevin And Fokker-Planck Analyses Of Inhibited Molecular Passing Processes Controlling Transport And Reactivity In Nanoporous Materials, Chi-Jen Wang, David Ackerman, Igor I. Slowing, James W. Evans

Ames Laboratory Publications

Inhibited passing of reactant and product molecules within the linear pores of nanoporous catalytic materials strongly reduces reactivity. The dependence of the passing propensity P on pore radius R is analyzed utilizing Langevin dynamics to account for solvent effects. We find that P∼(R−Rc)σ, where passing is sterically blocked for R≤Rc, with σ below the transition state theory value. Deeper insight comes from analysis of the corresponding high-dimensional Fokker-Planck equation, which facilitates an effective small-P approximation, and dimensional reduction enabling utilization of conformal mapping ideas. We analyze passing for spherical molecules and also assess the effect of ...


Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield Jun 2014

Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

We report in-plane thermoelectric power measurements on single crystals of (Ba1−xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x∼0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ∼75 K. Thermoelectric power also shows a change in the x∼0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition ...


Cold-Nuclear-Matter Effects On Heavy-Quark Production At Forward And Backward Rapidity In D + Au Collisions At Root S(Nn) = 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 Jun 2014

Cold-Nuclear-Matter Effects On Heavy-Quark Production At Forward And Backward Rapidity In D + Au Collisions At Root S(Nn) = 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

The PHENIX experiment has measured open heavy-flavor production via semileptonic decay over the transverse momentum range 1 < p(T) < 6 GeV/c at forward and backward rapidity (1.4 < vertical bar y vertical bar < 2.0) in d + Au and p + p collisions at root s(NN) = 200 GeV. In central d + Au collisions, relative to the yield in p + p collisions scaled by the number of binary nucleon-nucleon collisions, a suppression is observed at forward rapidity (in the d-going direction) and an enhancement at backward rapidity (in the Au-going direction). Predictions using nuclear-modified-parton-distribution functions, even with additional nuclear-p(T) broadening, cannot simultaneously reproduce the data at both rapidity ranges, which implies that these models are incomplete and suggests the possible importance of final-state interactions in the asymmetric d + Au collision system. These results can be used to probe cold-nuclear-matter effects, which may significantly affect heavy-quark production, in addition to helping constrain the magnitude of charmonia-breakup effects in nuclear matter.


Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield Jun 2014

Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield

Ames Laboratory Publications

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ABSTRACT

We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p∗∼1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p∗ up to 7.1 GPa. The T−p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p∗, a ...