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Iowa State University

2005

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Full-Text Articles in Physics

Theoretical Analysis Of Mound Slope Selection During Unstable Multilayer Growth, Maozhi Li, James W. Evans Dec 2005

Theoretical Analysis Of Mound Slope Selection During Unstable Multilayer Growth, Maozhi Li, James W. Evans

Mathematics Publications

A "step dynamics" model is developed for mound formation during multilayer homoepitaxy. Downward funneling of atoms deposited at step edges is incorporated and controls mound slope selection. Behavior of the selected slope differs from that predicted by phenomenological continuum treatments where the lateral mass current vanishes identically. Instead, this current is shown to vary periodically and vanish only on average. An exact coarse-grained continuum formulation with appropriate boundary conditions is derived and recovers step dynamics results.


Photonic Bandgaps Of Conformally Coated Structures, Rana Biswas, Jinho Ahn, Taoho Lee, Jae-Hwang Lee, Yong-Sung Kim, Chang-Hwan Kim, Wai Y. Leung, Cha-Hwan Oh, Kristen P. Constant, Kai-Ming Ho Dec 2005

Photonic Bandgaps Of Conformally Coated Structures, Rana Biswas, Jinho Ahn, Taoho Lee, Jae-Hwang Lee, Yong-Sung Kim, Chang-Hwan Kim, Wai Y. Leung, Cha-Hwan Oh, Kristen P. Constant, Kai-Ming Ho

Materials Science and Engineering Publications

Polymeric molds of the layer-by-layer photonic crystal can be economically synthesized with a microtransfer molding technique. The refractive indices of these molds are low, preventing formation of a photonic bandgap. We find that such molds can be conformally coated with higher-index material. Photonic band calculations find structures in which conformally coated layer-by-layer molds have complete bandgaps for both titania and silicon coatings. Large stop bands exist in the 001 stacking direction. Feasibility of experimental conformal coating of the molds has been demonstrated with a titania-coated polyurethane mold, which shows optical features in agreement with simulations of reflection and transmission.


Compositional Variation Of The Phonon Dispersion Curves Of Bcc Fe-Ga Alloys, Jerel L. Zarestky, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis Nov 2005

Compositional Variation Of The Phonon Dispersion Curves Of Bcc Fe-Ga Alloys, Jerel L. Zarestky, V. O. Garlea, Thomas A. Lograsso, Deborah L. Schlagel, C. Stassis

Ames Laboratory Publications

Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of bcc Fe1−xGax (x=10.8, 13.3, 16.0, 22.5) alloys as a function of Ga concentration. The phonon frequencies of every branch were found to decrease significantly with increasing Ga concentration. The softening was most pronounced for the T2[ξξ0] branch and, to a lesser extent, the L[ξξξ] branch in the vicinity of ξ=2/3. The concentration dependence of the shear elastic constant C′=1∕2(C11−C12), calculated from the slope of the T ...


Fe–Ga/Pb(Mg1/3nb2/3)O3–Pbtio3 Magnetoelectric Laminate Composites, Shuxiang Dong, Junyi Zhai, Naigang Wang, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso Nov 2005

Fe–Ga/Pb(Mg1/3nb2/3)O3–Pbtio3 Magnetoelectric Laminate Composites, Shuxiang Dong, Junyi Zhai, Naigang Wang, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso

Ames Laboratory Publications

We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe–20%Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or1.01 V/cm Oe). Near the natural resonant frequency ( ∼ 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe)for the L-L mode. In ...


Measurement Of Transverse Single-Spin Asymmetries For Midrapidity Production Of Neutral Pions And Charged Hadrons In Polarized P+P Collisions At √S=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al. Nov 2005

Measurement Of Transverse Single-Spin Asymmetries For Midrapidity Production Of Neutral Pions And Charged Hadrons In Polarized P+P Collisions At √S=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al.

Physics and Astronomy Publications

Transverse single-spin asymmetries to probe the transverse-spin structure of the proton have been measured for neutral pions and nonidentified charged hadrons from polarized proton-proton collisions at midrapidity and √s=200  GeV. The data cover a transverse momentum (pT) range 1.0–5.0  GeV/c for neutral pions and 0.5–5.0  GeV/c for charged hadrons, at a Feynman-x value of approximately zero. The asymmetries seen in this previously unexplored kinematic region are consistent with zero within errors of a few percent. In addition, the inclusive charged hadron cross section at midrapidity from 0.5


Magnetostructural Transition And Magnetocaloric Effect In Ni55mn20ga25 Single Crystals, M. Pasquale, C. P. Sasso, L. H. Lewis, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel Sep 2005

Magnetostructural Transition And Magnetocaloric Effect In Ni55mn20ga25 Single Crystals, M. Pasquale, C. P. Sasso, L. H. Lewis, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

A first order transition from a paramagnetic-austenite phase to a ferromagnetic-martensite phase occurring in off-stoichiometry single crystals of Ni2MnGa at 313 K presents unique features due to the multifunctional character of the magnetic shape memory alloy. A remarkable magnetocaloric effect, associated with an entropy change up to ΔS≈−86 J kg−1 K−1 and an adiabatic temperature change ΔT≈2.2 K, accompanied by mechanical strain Δε⩾3% have been observed in samples subjected to changes of the applied magnetic field ΔH=4×106 A∕m (≈5 T). The effects of magnetic field, temperature, and stress on ...


Steady States Of A Nonequilibrium Lattice Gas, Edward Lyman, Beate Schmittmann Sep 2005

Steady States Of A Nonequilibrium Lattice Gas, Edward Lyman, Beate Schmittmann

Beate Schmittmann

We present a Monte Carlo study of a lattice gas driven out of equilibrium by a local hopping bias. Sites can be empty or occupied by one of two types of particles, which are distinguished by their response to the hopping bias. All particles interact via excluded volume and a nearest-neighbor attractive force. The main result is a phase diagram with three phases: a homogeneous phase and two distinct ordered phases. Continuous boundaries separate the homogeneous phase from the ordered phases, and a first-order line separates the two ordered phases. The three lines merge in a nonequilibrium bicritical point.


Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis Sep 2005

Neutron Diffraction Studies Of The Magnetoelastic Compounds Tb5sixge4−X (X=2.2 And 2.5), V. O. Garlea, Jerel L. Zarestky, C. Y. Jones, L.-L. Lin, Deborah L. Schlagel, Thomas A. Lograsso, A. O. Tsokol, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., C. Stassis

Ames Laboratory Publications

We report the results of a neutron diffraction study, carried out on both single crystalline and polycrystalline samples of Tb5Si2.2Ge1.8 and polycrystalline Tb5Si2.5Ge1.5. On cooling, at approximately 120 K, the Tb5Si2.2Ge1.8 system undergoes a magnetoelastic transition from a high-temperature monoclinic-paramagnetic to a low-temperature orthorhombic-ferromagnetic structure. Between 120 K and 75 K, the magnetic structure has a net ferromagnetic component along the a axis direction. The moments are slightly canted with respect to the a axis, while the components along ...


Systematic, Multisite Short-Range-Order Corrections To The Electronic Structure Of Disordered Alloys From First Principles: The Kkr Nonlocal Cpa From The Dynamical Cluster Approximation, D. A. Biava, Subhradip Ghosh, Duane D. Johnson, W. A. Shelton, Andrei V. Smirnov Sep 2005

Systematic, Multisite Short-Range-Order Corrections To The Electronic Structure Of Disordered Alloys From First Principles: The Kkr Nonlocal Cpa From The Dynamical Cluster Approximation, D. A. Biava, Subhradip Ghosh, Duane D. Johnson, W. A. Shelton, Andrei V. Smirnov

Duane D. Johnson

Although the Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) is used widely to configurationally average and get electronic structures and energies of disordered alloys, a single-site CPA misses local environment effects, including short-range order (SRO). A proposed nonlocal CPA (NLCPA) recovers translational invariance of the effective medium via k-space coarse graining from the dynamical cluster approximation (DCA), where corrections are systematic as cluster size increases. We implement a first-principles KKR-NLCPA/DCA and show the effects of environment, including SRO, on the electronic structures of fcc CuAu and bcc NiAl.


Genetic Programming For Multitimescale Modeling, Kumara Sastry, Duane D. Johnson, David E. Goldberg, Pascal Bellon Aug 2005

Genetic Programming For Multitimescale Modeling, Kumara Sastry, Duane D. Johnson, David E. Goldberg, Pascal Bellon

Duane D. Johnson

A bottleneck for multitimescale thermally activated dynamics is the computation of the potential energy surface. We explore the use of genetic programming (GP) to symbolically regress a mapping of the saddle-point barriers from only a few calculated points via molecular dynamics, thereby avoiding explicit calculation of all barriers. The GP-regressed barrier function enables use of kinetic Monte Carlo to simulate real-time kinetics (seconds to hours) based upon realistic atomic interactions. To illustrate the concept, we apply a GP regression to vacancy-assisted migration on a surface of a concentrated binary alloy (from both quantum and empirical potentials) and predict the diffusion ...


Measurement Of Single Electron Event Anisotropy In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Aug 2005

Measurement Of Single Electron Event Anisotropy In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The transverse momentum dependence of the azimuthal anisotropy parameter v(2), the second harmonic of the azimuthal distribution, for electrons at midrapidity (vertical bar eta vertical bar < 0.35) has been measured with the PHENIX detector in Au+Au collisions at root s(NN) = 200 GeV. The measurement was made with respect to the reaction plane defined at high rapidities (vertical bar eta vertical bar = 3.1-3.9). From the result we have measured the v(2) of electrons from heavy flavor decay after subtraction of the v(2) of electrons from other sources such as photon conversions and Dalitz decay from light neutral mesons. We observe a nonzero single electron v(2) with a 90% confidence level in the intermediate-p(T) region. The precision of the present data set does not permit us to conclude definitively that heavy quarks exhibit thermalization with the transverse flow of the bulk matter.


Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso Jul 2005

Magnetic Force Microscopy Investigation Of Domain Structures In Fe–X At. % Ga Single Crystals (12, Feiming Bai, Jiefang Li, D. Viehland, D. Wu, Thomas A. Lograsso

Ames Laboratory Publications

The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe–x at. % Ga (x = 12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe–12 at. % Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe–20 at. % Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions—in the PA condition, clear dendritic domains were observed. For both FC and PA Fe–25 at. % Ga, a much reduced [100] preferred domain orientation was found, the domain size ...


Real-Space Observation Of Quasicrystalline Sn Monolayer Formed On The Fivefold Surface Of Icosahedral AlCuFe Quasicrystal, H. R. Sharma, M. Shimoda, A. R. Ross, Thomas A. Lograsso, A. P. Tsai Jul 2005

Real-Space Observation Of Quasicrystalline Sn Monolayer Formed On The Fivefold Surface Of Icosahedral AlCuFe Quasicrystal, H. R. Sharma, M. Shimoda, A. R. Ross, Thomas A. Lograsso, A. P. Tsai

Ames Laboratory Publications

We investigate a thin Sn film grown at elevated temperatures on the fivefold surface of an icosahedral AlCuFe quasicrystal by scanning tunneling microscopy (STM). At about one monolayer coverage, the deposited Sn is found to form a smooth film of height consistent with one-half of the lattice constant of the bulk Sn. Analysis based on the Fourier transform and autocorrelation function derived from high-resolution STM images reveals that Sn grows pseudomorphically and hence exhibits a quasicrystalline structure.


Hydrostatic Pressure Control Of The Magnetostructural Phase Transition In Gd5si2ge2 Single Crystals, C. Magen, L. Morellon, P. A. Algarabel, M. R. Ibarra, Z. Arnold, J. Kamarad, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, A. O. Tsokol, Karl A. Gschneidner Jr. Jul 2005

Hydrostatic Pressure Control Of The Magnetostructural Phase Transition In Gd5si2ge2 Single Crystals, C. Magen, L. Morellon, P. A. Algarabel, M. R. Ibarra, Z. Arnold, J. Kamarad, Thomas A. Lograsso, Deborah L. Schlagel, Vitalij K. Pecharsky, A. O. Tsokol, Karl A. Gschneidner Jr.

Ames Laboratory Publications

Magnetic and structural properties of single crystalline Gd5Si2Ge2 under hydrostatic pressure have been characterized by using magnetization, linear thermal expansion, and compressibility measurements. A strong dependence of Curie temperature on pressure, dTC∕dP=+4.8 K∕kbar, is observed in contrast with the smaller values of about 3 K∕kbar found in polycrystalline specimens. This difference reflects the role the microstructure may play in pressure-induced magnetic-crystallographic phase changes, likely related to stress relaxation at the grain boundaries, domain pinning and/or nucleation of defects. The pressure dependence of the critical magnetic field, d(dH ...


Copper Adsorption On The Fivefold Al70pd21mn9 Quasicrystal Surface, J. Ledieu, J. T. Hoeft, D. E. Reid, J. A. Smerdon, R. D. Diehl, N. Ferralis, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Jul 2005

Copper Adsorption On The Fivefold Al70pd21mn9 Quasicrystal Surface, J. Ledieu, J. T. Hoeft, D. E. Reid, J. A. Smerdon, R. D. Diehl, N. Ferralis, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

Recently we reported the formation of a quasiperiodic Cu thin film on the fivefold icosahedral Al-Pd-Mn quasicrystal using scanning tunneling microscopy, low energy electron diffraction, and Auger electron spectroscopy. Here we provide details pertaining to the growth, stability, and structure of this film. Structural information has been gained by LEED measurements carried out at 85 K. Cu atoms are organized periodically with a nearest-neighbor distance of 2.5±0.1 Å along the aperiodically spaced rows. Above 8 ML spontaneous mass transport resulting in island formation has been observed by STM. These observations point to ascending adatoms being responsible for ...


Production Of Phi Mesons At Midrapidity In Root S-Nn=200 Gevau+Au Collisions At Relativistic Energies, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Jul 2005

Production Of Phi Mesons At Midrapidity In Root S-Nn=200 Gevau+Au Collisions At Relativistic Energies, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present the results of phi meson production in the K+K- decay channel from Au+Au collisions at root s(NN) =200 GeV as measured at midrapidity by the PHENIX detector at Brookhaven National Laboratory's Relativistic Heavy Ion Collider. Precision resonance centroid and width values are extracted as a function of collision centrality. No significant variation from the Particle Data Group accepted values is observed, contrary to some model predictions. The phi transverse mass spectra are fitted with a linear exponential function for which the derived inverse slope parameter is seen to be constant as a function of ...


Magnetic Properties Of Single-Crystal Dyal2, A. L. Lima, A. O. Tsokol, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Thomas A. Lograsso, Deborah L. Schlagel Jul 2005

Magnetic Properties Of Single-Crystal Dyal2, A. L. Lima, A. O. Tsokol, Karl A. Gschneidner Jr., Vitalij K. Pecharsky, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

We measured the magnetic properties and heat capacity of three DyAl2 single crystals with the magnetic field oriented along the three principal crystallographic directions: [100], [110], and [111]. The isothermal entropy change versus temperature curves were obtained from heat capacity and magnetization data for these directions. The experimental results were successfully explained by a mean field model that includes spin reorientation, exchange interactions, and crystalline electric field effects. The anomalous magnetocaloric effect along the [111] direction predicted by theory was confirmed experimentally.


Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr. Jun 2005

Magnetic Structure Of Gd5ge4, L. Tan, Andreas Kreyssig, J. W. Kim, Alan I. Goldman, Robert J. Mcqueeney, D. Wermeille, B. Sieve, Thomas A. Lograsso, Deborah L. Schlagel, Sergey L. Bud'ko, Vitalij K. Pecharsky, Karl A. Gschneidner Jr.

Ames Laboratory Publications

Gd5Ge4 crystallizes in the orthorhombic space group Pnma, and orders antiferromagnetically below the Néel temperatureTN∼127 K. We have employed x-ray resonant magnetic scattering to elucidate the details of the magnetic structure. The magnetic unit cell is the same as the chemical unit cell. From azimuth scans and the Q dependence of the magnetic scattering, all three Gd sites in the structure were determined to be in the same magnetic space group Pnm′a. The magnetic moments are primarily aligned along the c axis and the c components of the magnetic moments at the three different ...


Rheed And Stm Studies Of The Pseudo-Tenfold Surface Of The Ξ′-Al77.5pd19mn3.5 Approximant Crystal, H. R. Sharma, M. Shimoda, V. Fournée, Thomas A. Lograsso, A. P. Tsai Jun 2005

Rheed And Stm Studies Of The Pseudo-Tenfold Surface Of The Ξ′-Al77.5pd19mn3.5 Approximant Crystal, H. R. Sharma, M. Shimoda, V. Fournée, Thomas A. Lograsso, A. P. Tsai

Ames Laboratory Publications

The pseudo-tenfold surface of the ξ′-Al77.5Pd19Mn3.5 crystal, an approximant of the icosahedral Al–Pd–Mn quasicrystal, is investigated by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy. The observed RHEED patterns of the surface after sputtering are found to be consistent with those of a simple cubic lattice with (11̅ 0) surface plane. The [001] and [110] axes of the surface plane are oriented along the principal low-index axes of the bulk. The RHEED patterns of the sputter-annealed surface consist of diffraction streaks with periodic spacings expected for the bulk truncated ...


Centrality Dependence Of Direct Photon Production In Root S-Nn=200 Gev Au+Au Collisions, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Jun 2005

Centrality Dependence Of Direct Photon Production In Root S-Nn=200 Gev Au+Au Collisions, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Jan Rak, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The first measurement of direct photons in Au+Au collisions at root s(NN)=200 GeV is presented. The direct photon signal is extracted as a function of the Au+Au collision centrality and compared to next-to-leading order perturbative quantum chromodynamics calculations. The direct photon yield is shown to scale with the number of nucleon-nucleon collisions for all centralities.


Saturation Of Azimuthal Anisotropy In Au Plus Au Collisions At Root S-Nn=62-200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, F. K. Wohn, Et Al., Phenix Collaboration Jun 2005

Saturation Of Azimuthal Anisotropy In Au Plus Au Collisions At Root S-Nn=62-200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

New measurements are presented for charged hadron azimuthal correlations at midrapidity in Au+Au collisions at root s(NN)=62.4 and 200 GeV. They are compared to earlier measurements obtained at root s(NN)=130 GeV and in Pb+Pb collisions at root s(NN)=17.2 GeV. Sizeable anisotropies are observed with centrality and transverse momentum (p(T)) dependence characteristic of elliptic flow (v(2)). For a broad range of centralities, the observed magnitudes and trends of the differential anisotropy, v(2)(p(T)), change very little over the collision energy range root s(NN)=62-200 GeV, indicating ...


Gas Holdup In Opaque Cellulose Fiber Slurries, Sarah M. Talcott, Theodore J. Heindel Jun 2005

Gas Holdup In Opaque Cellulose Fiber Slurries, Sarah M. Talcott, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Three different cellulose fiber types are used to study their effect on gas holdup and flow regime transition in a 10.2 cm semi-batch bubble column. The three natural fiber types include bleached softwood chemical pulp (softwood), bleached hardwood chemical pulp (hardwood), and bleached softwood chemithermomechanical pulp (BCTMP). Gas holdup is recorded over a range of fiber mass fractions (0 ≤ C ≤ 1.6%) and superficial gas velocities (Ug ≤ 23 cm/s). Experimental results show that gas holdup decreases with increasing fiber mass fraction. Homogeneous, transitional, and heterogeneous flow is observed for all three fiber types at low fiber mass fractions ...


Using X-Rays For Multiphase Flow Visualization, Theodore J. Heindel, Jeremy L. Hubers, Terrence C. Jensen, Joseph N. Gray, Alexander C. Stiegel Jun 2005

Using X-Rays For Multiphase Flow Visualization, Theodore J. Heindel, Jeremy L. Hubers, Terrence C. Jensen, Joseph N. Gray, Alexander C. Stiegel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Gas-liquid, gas-solid, liquid-solid, and gas-liquid-solid multiphase flows are difficult to visualize, characterize, and quantify because the systems are typically opaque. Invasive or noninvasive measurement methods are typically used for determining internal flow and transport characteristics of these complex flows. The difficulty with invasive methods is that they can alter the internal flow of a multiphase system causing interference with realistic process measurements. X-ray imaging provides one family of noninvasive measurement techniques used extensively for product testing and evaluation of static objects with complex structures. These techniques have been extended to visualize dynamic systems, such as those which characterize multiphase flows ...


Exact Dynamics Of A Reaction-Diffusion Model With Spatially Alternating Rates, M. Mobilia, Beate Schmittmann, R. K. P. Zia May 2005

Exact Dynamics Of A Reaction-Diffusion Model With Spatially Alternating Rates, M. Mobilia, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We present the exact solution for the full dynamics of a nonequilibrium spin chain and its dual reaction-diffusion model, for arbitrary initial conditions. The spin chain is driven out of equilibrium by coupling alternating spins to two thermal baths at different temperatures. In the reaction-diffusion model, this translates into spatially alternating rates for particle creation and annihilation, and even negative “temperatures” have a perfectly natural interpretation. Observables of interest include the magnetization, the particle density, and all correlation functions for both models. Two generic types of time dependence are found: if both temperatures are positive, the magnetization, density, and correlation ...


Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Thermal Expansion And Gruneisen Parameters In Some Pr–Ni–Si Compounds, S. H. Song, David C. Jiles, J. E. Snyder, A. O. Pecharsky, D. Wu, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

In this study, the thermal expansion and Gruneisen parameter of polycrystalline “Pr5Ni2Si3” and “Pr15Ni7Si10” were investigated over the temperature range of 5–300 K. Calculations of the phonon contribution to thermal expansion were made, which allowed the magnetic contribution to thermal expansion to be calculated from the difference between the total thermal expansion and the phonon contribution. This resulted in a temperature-dependent magnetic contribution to thermal expansion that varied with the magnetic ordering of the material. The results show two magnetic transitions in each compound, the higher temperature transition corresponding ...


Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark May 2005

Magnetic Field Dependence Of Galfenol Elastic Properties, G. Petculescu, K. B. Hathaway, Thomas A. Lograsso, M. Wun-Fogle, A. E. Clark

Ames Laboratory Conference Papers, Posters, and Presentations

Elastic shear moduli measurements on Fe100−xGax (x = 12–33) single crystals (via resonant ultrasound spectroscopy) with and without a magnetic field and within 4–300 K are reported. The pronounced softening of the tetragonal shear modulus c′ is concluded to be, based on magnetoelastic coupling, the cause of the second peak in the tetragonal magnetostriction constant λ100 near x = 28. Exceedingly high ΔE effects ( ∼ 25%), combined with the extreme softness in c′ (c′<10 GPa), suggest structural changes take place, yet, gradual in nature, as the moduli show a smooth dependence on Ga concentration, temperature, and magnetic field. Shear anisotropy (c44/c′) as high as 14.7 was observed for Fe71.2Ga28.8.


Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum May 2005

Temperature Dependence Of The Magnetic Anisotropy And Magnetostriction Of Fe100−Xgax (X = 8.6, 16.6, 28.5), A. E. Clark, M. Wun-Fogle, J. B. Restorff, Kevin W. Dennis, Thomas A. Lograsso, R. William Mccallum

Ames Laboratory Conference Papers, Posters, and Presentations

The temperature dependence of the lowest order magnetic anisotropy constant K1 and the lowest order saturation magnetostriction constant, (3/2)λ100, were measured from 4 K to 300 K for Fe91.4Ga8.6,Fe83.4Ga16.6, and Fe71.5Ga28.5 and were compared to the normalized magnetization power law, ml(l+1)/2. Fe91.4Ga8.6 maintains the magnetostriction anomaly of Fe (dλ100/dT>0) and K1 is a reasonable fit to the ml(l+1)/2power law with ...


Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles May 2005

Magnetic Anisotropy And Phase Transitions In Single-Crystal Tb5(Si2.2ge1.8), M. Han, J. E. Snyder, W. Tang, Thomas A. Lograsso, Deborah L. Schlagel, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

The Tb5(SixGe4−x) alloy system has many features in common with the Gd5(SixGe4−x)system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystalTb5(Si2.2Ge1.8) which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1/χ vs T indicates that there is a transition from paramagnetic to ferromagnetic at Tc = 110 K. Below this ...


Jet Structure Of Baryon Excess In Au+Au Collisions At Root Snn=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration May 2005

Jet Structure Of Baryon Excess In Au+Au Collisions At Root Snn=200 Gev, S. S. Adler, Sergey Belikov, S. Bhagavatula, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Two particle correlations between identified meson and baryon trigger particles with 2.5 < p (T)(T)(<4.0 GeV/c and lower p ) (charged hadrons have been measured at midrapidity by the PHENIX experiment at RHIC in p+p,d+Au, and Au+Au collisions at s)(NN) = 200 GeV. In noncentral Au+Au collisions, the probability of finding a hadron near in azimuthal angle to the trigger particles is almost identical for mesons and baryons and significantly higher than in p+p collisions. The associated yields for trigger baryons decrease in the most central collisions, consistent with some baryon production by thermal recombination in addition to hard scattering.


Magnetostrictive And Magnetoelectric Behavior Of Fe–20 At. % Ga/Pb(Zr,Ti)O3 Laminates, Shuxiang Dong, Junyi Zhai, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso Apr 2005

Magnetostrictive And Magnetoelectric Behavior Of Fe–20 At. % Ga/Pb(Zr,Ti)O3 Laminates, Shuxiang Dong, Junyi Zhai, Feiming Bai, Jiefang Li, D. Viehland, Thomas A. Lograsso

Ames Laboratory Publications

The magnetostrictive and magnetoelectric (ME) properties of laminate composites of Fe–20 at. % Ga and Pb(Zr,Ti)O3 (PZT) have been studied for laminates of different geometries. The results show that (i) a long-type magnetostrictive Fe–20 at. % Ga crystal plate oriented along 〈001〉c and magnetized in its longitudinal (or length) direction has higher magnetostriction than a disk-type one; and consequently (ii) a long-type Fe–20 at. % Ga/PZT laminate has a giant ME effect, and is sensitive to low-level magnetic fields.