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Iowa State University

2002

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Articles 1 - 30 of 41

Full-Text Articles in Physics

Bulk Termination Of The Quasicrystalline Fivefold Surface Of Al70pd21mn9, Z. Papadopolos, G. Kasner, J. Ledieu, E. J. Cox, N. V. Richardson, Q. Chen, R. D. Diehl, Thomas A. Lograsso, A. R. Ross, R. Mcgrath Nov 2002

Bulk Termination Of The Quasicrystalline Fivefold Surface Of Al70pd21mn9, Z. Papadopolos, G. Kasner, J. Ledieu, E. J. Cox, N. V. Richardson, Q. Chen, R. D. Diehl, Thomas A. Lograsso, A. R. Ross, R. Mcgrath

Ames Laboratory Publications

The structure of the Al70Pd21Mn9 surface has been investigated using high-resolution scanning tunneling microscopy. From two large fivefold terraces on the surface in a short decorated Fibonacci sequence, atomically resolved surface images have been obtained. One of these terraces carries a rare local configuration in the form of a ring. The location of the corresponding sequence of terminations in the bulk model M of icosahedral i-AlPdMn based on the three-dimensional tiling T*(2F) of an F phase has been estimated using this ring configuration and the requirement from low-energy electron diffraction work of Gierer et ...


Linear Thermal Expansivity (1–300 K), Specific Heat (1–108 K), And Electrical Resistivity Of The Icosahedral Quasicrystal I-Al61.4cu25.4fe13.2, Clayton A. Swenson, Thomas A. Lograsso, A. R. Ross, N. E. Anderson Jr. Nov 2002

Linear Thermal Expansivity (1–300 K), Specific Heat (1–108 K), And Electrical Resistivity Of The Icosahedral Quasicrystal I-Al61.4cu25.4fe13.2, Clayton A. Swenson, Thomas A. Lograsso, A. R. Ross, N. E. Anderson Jr.

Ames Laboratory Publications

Linear thermal expansivity (α, 1–300 K), heat capacity (Cp, 1–108 K), and electrical resistivity (ρ, 1–300 K) measurements are reported for single grain i-Al61.4Cu25.4Fe13.2 quasicrystals as a function of sample processing. While ρ(T) is sensitive to sample treatment, both Cp and α are relatively insensitive (to a few percent) except at the lowest temperatures (below 4 K), where an inverse correlation between ρ and the electronic Cp coefficient γ appears to exist. Dispersion effects (deviations from Debye-like behavior) in both Cp and the lattice ...


Flow Measurements Via Two-Particle Azimuthal Correlations In Au Plus Au Collisions At Root S-Nn=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Nov 2002

Flow Measurements Via Two-Particle Azimuthal Correlations In Au Plus Au Collisions At Root S-Nn=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Two-particle azimuthal correlation functions are presented for charged hadrons produced in Au + Au collisions at the Relativistic Heavy Ion Collider (roots(NN) = 130 GeV). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values (upsilon(2)) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone epsilon, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low p(T). A breakdown of ...


Stationary Correlations For A Far-From-Equilibrium Spin Chain, Beate Schmittmann, F. Schmüser Oct 2002

Stationary Correlations For A Far-From-Equilibrium Spin Chain, Beate Schmittmann, F. Schmüser

Beate Schmittmann

A kinetic one-dimensional Ising model on a ring evolves according to a generalization of Glauber rates, such that spins at even (odd) lattice sites experience a temperature Te (To). Detailed balance is violated so that the spin chain settles into a nonequilibrium stationary state, characterized by multiple interactions of increasing range and spin order. We derive the equations of motion for arbitrary correlation functions and solve them to obtain an exact representation of the steady state. Two nontrivial amplitudes reflect the sublattice symmetries; otherwise, correlations decay exponentially, modulo the periodicity of the ring. In the long-chain limit, they factorize into ...


Structural Studies Of Fe0.81ga0.19 By Reciprocal Space Mapping, D. Viehland, Jiefang Li, Thomas A. Lograsso, A. R. Ross, Manfred Wuttig Oct 2002

Structural Studies Of Fe0.81ga0.19 By Reciprocal Space Mapping, D. Viehland, Jiefang Li, Thomas A. Lograsso, A. R. Ross, Manfred Wuttig

Ames Laboratory Publications

Reciprocal lattice mapping has been performed on Fe0.81Ga0.19 crystals by ω–ω/2θ, Ψ–ϕ, and ω–ϕ scans. A strong elongation of the 〈001〉c peak was found along the〈110〉c direction. ω scans revealed short lateral correlation lengths ξ along 〈110〉cand strong diffuse scattering along the 〈001〉c. Multiple domains with monoclinic symmetry (angle ∼190°) were observed by Ψ–ϕ and ω–ϕ scans on the (001)c face, and were also tilted with respect to each other. The results show an average cubic structure with orthorhombic structural modulations, and ...


Fluctuations And Bistability In A "Hybrid" Atomistic Model For Co Oxidation On Nanofacets: An Effective Potential Analysis, Da-Jiang Liu, James W. Evans Oct 2002

Fluctuations And Bistability In A "Hybrid" Atomistic Model For Co Oxidation On Nanofacets: An Effective Potential Analysis, Da-Jiang Liu, James W. Evans

Mathematics Publications

An analysis on the existence of bistability in the hybrid reaction model for CO oxidation in finite systems is demonstrated. As such, numerical evidence to indicate the existence of an effective potential characterizing this behavior is provided. This potential is determined by exact kinetic Monte Carlo (KMC) simulation analysis, but reasonable estimate available from approximate master equations, and from Fokker-Planck equations which are obtained from further approximation of the master equations.


Sintering Of Two-Dimensional Nanoclusters In Metal(100) Homoepitaxial Systems: Deviations From Predictions Of Mullins Continuum Theory, Da-Jiang Liu, James W. Evans Oct 2002

Sintering Of Two-Dimensional Nanoclusters In Metal(100) Homoepitaxial Systems: Deviations From Predictions Of Mullins Continuum Theory, Da-Jiang Liu, James W. Evans

Mathematics Publications

We present a comparison of the predictions of atomistic and continuum models for the sintering of pairs of near-square two-dimensional nanoclusters adsorbed on the (100) surface in fcc metal homoepitaxial systems. Mass transport underlying these processes is dominated by periphery diffusion (PD) of adatoms along the edge of the clusters. A Mullins-type continuum model for cluster evolution incorporates anisotropy in the step edge stiffness (reflecting the energetics and adsorption site lattice structure in the atomistic model), and can also account for anisotropy in the step edge mobility (reflecting details of the kinetics). In such continuum treatments, the characteristic time τeqfor ...


Simulation Of Chemical Mechanical Planarization Of Copper With Molecular Dynamics, Y. Ye, Rana Biswas, Ashraf F. Bastawros, Abhijit Chandra Sep 2002

Simulation Of Chemical Mechanical Planarization Of Copper With Molecular Dynamics, Y. Ye, Rana Biswas, Ashraf F. Bastawros, Abhijit Chandra

Aerospace Engineering Publications

With an aim to understanding the fundamental mechanisms underlying chemical mechanical planarization ~CMP! of copper, we simulate the nanoscale polishing of a copper surface with molecular dynamics utilizing the embedded atom method. Mechanical abrasion produces rough planarized surfaces with a large chip in front of the abrasive particle, and dislocations in the bulk of the crystal. The addition of chemical dissolution leads to very smooth planarized copper surfaces and considerably smaller frictional forces that prevent the formation of bulk dislocations. This is a first step towards understanding the interplay between mechanistic material abrasion and chemical dissolution in chemical mechanical planarization ...


Heisenberg Spin Triangles In {V6}-Type Magnetic Molecules: Experiment And Theory, Marshall Luban, Ferdinando Borsa, Sergey L. Bud'ko, Paul C. Canfield, Suckjoon Jun, Jae Kap Jung, Paul Kögerler, Detlef Mentrup, Achim Müller, Robert Modler, Daniel Procissi, Byoung Jin Suh, Milton S. Torikachvili Aug 2002

Heisenberg Spin Triangles In {V6}-Type Magnetic Molecules: Experiment And Theory, Marshall Luban, Ferdinando Borsa, Sergey L. Bud'ko, Paul C. Canfield, Suckjoon Jun, Jae Kap Jung, Paul Kögerler, Detlef Mentrup, Achim Müller, Robert Modler, Daniel Procissi, Byoung Jin Suh, Milton S. Torikachvili

Ames Laboratory Publications

We report the results of systematic experimental and theoretical studies of two closely related species of magnetic molecules of the type {V6}, where each molecule includes a pair of triangles of exchange-coupled vanadyl (VO2+,spin s=1/2) ions. The experimental studies include the temperature dependence of the low-field susceptibility from room temperature down to 2 K, the dependence of the magnetization on magnetic field up to 60 T for several low temperatures, the temperature dependence of the magnetic contribution to the specific heat, and the 1H and 23Nanuclear magnetic resonance spin-lattice relaxation rates 1/T1. This body of experimental ...


Event-By-Event Fluctuations In Mean P(T) And Mean E(T) In Root S(Nn)=130 Gev Au+Au Collisions, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Aug 2002

Event-By-Event Fluctuations In Mean P(T) And Mean E(T) In Root S(Nn)=130 Gev Au+Au Collisions, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at roots(NN)=130 GeV at the Relativistic Heavy-Ion Collider. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of nonstatistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant nonrandom fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p(T) or e(T) spectra, we exclude a region ...


Net Charge Fluctuations In Au+Au Interactions Root S(Nn)=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Aug 2002

Net Charge Fluctuations In Au+Au Interactions Root S(Nn)=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Data from Au+Au interactions at s(NN)=130 GeV, obtained with the PHENIX detector at the Relativistic Heavy-Ion Collider, are used to investigate local net charge fluctuations among particles produced near midrapidity. According to recent suggestions, such fluctuations may carry information from the quark-gluon plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays.


Measurement Of Lambda And Anti-Lambda Particles In Au Plus Au Collisions At Root S(Nn)=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios N. Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Aug 2002

Measurement Of Lambda And Anti-Lambda Particles In Au Plus Au Collisions At Root S(Nn)=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios N. Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present results on the measurement of Lambda and Anti-Lambda production in Au+Au collisions at root s(NN)=130 GeV with the PHENIX detector at the Relativistic Heavy Ion Collider. The transverse momentum spectra were measured for minimum bias and for the 5% most central events. The Anti-Lambda/Lambda ratios are constant as a function of p(T) and the number of participants. The measured net Lambda density is significantly larger than predicted by models based on hadronic strings (e.g., HIJING) but in approximate agreement with models which include the gluon-junction mechanism.


Magnetochemical Origin For Invar Anomalies In Iron-Nickel Alloys, V. Crisan, P. Entel, H. Ebert, H. Akai, Duane D. Johnson, J. B. Staunton Jul 2002

Magnetochemical Origin For Invar Anomalies In Iron-Nickel Alloys, V. Crisan, P. Entel, H. Ebert, H. Akai, Duane D. Johnson, J. B. Staunton

Duane D. Johnson

Zero- and finite-temperature (T) first-principles calculations versus composition (c) show that magnetochemical effects lead to Invar anomalies in Fe-(Ni, Co, Pt) alloys. Chemical short- or long-range order and negative interatomic exchange interaction of electrons in antibonding majority-spin states force the face-centered-cubic lattice to compete simultaneously for a smaller volume (from antiferromagnetic tendencies) and a larger volume (from Stoner ferromagnetic tendencies). The resulting additional negative lattice anharmonicity is very large for Fe-(Ni, Co) while absent for Fe-Pt. Our results explain the T- and c-dependent behavior of Invar properties, including the lattice softening and thermal expansion of Fe-Ni. In addition ...


Centrality Dependence Of Pi(+/-), K-+/-, P, And (P)Over-Bar Production From Root(Nn)-N-S = 130 Gev Au+Au Collisions At Rhic, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration Jun 2002

Centrality Dependence Of Pi(+/-), K-+/-, P, And (P)Over-Bar Production From Root(Nn)-N-S = 130 Gev Au+Au Collisions At Rhic, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Identified pi(+/-), K+/-, p, and (p) over bar transverse momentum spectra at midrapidity in root s(NN) = 130 GeV Au + Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K+/-, p, and (p) over bar yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta ...


Morphological Evolution Of The Fivefold Surface Of I-Alpdmn Quasicrystals, Giovanni Cappello, Joël Chevrier, Frank Schmithüsen, Andreas Stierle, Vincenzo Formoso, Fabio Comin, Marc De Boissieu, Michel Boudard, Thomas A. Lograsso, Cynthia J. Jenks, Dwight Delaney May 2002

Morphological Evolution Of The Fivefold Surface Of I-Alpdmn Quasicrystals, Giovanni Cappello, Joël Chevrier, Frank Schmithüsen, Andreas Stierle, Vincenzo Formoso, Fabio Comin, Marc De Boissieu, Michel Boudard, Thomas A. Lograsso, Cynthia J. Jenks, Dwight Delaney

Ames Laboratory Publications

Morphology of the fivefold symmetric quasicrystal surface of AlPdMn was investigated by x-ray reflectivity and by x-ray diffraction. X-ray experiments revealed two different morphologies depending on the surface preparation. Sputtering and annealing up to 900 K, under UHV conditions, produced a rough and facetted quasicrystal surface. These features were confirmed by atomic force microscopy and scanning tunnel microscopy measurements. We also observed that an annealing above 900 K induces a rapid and irreversible transition toward a flat surface.


Quadrupolar And Dipolar Contributions To X-Ray Magnetic Circular Dichroism At The Tb L3,2 Edges: Experiment Versus Theory, H. Wende, Z. Li, A. Scherz, G. Ceballos, K. Baberschke, A. Ankudinov, J. J. Rehr, F. Wilhelm, A. Rogalev, Deborah L. Schlagel, Thomas A. Lograsso May 2002

Quadrupolar And Dipolar Contributions To X-Ray Magnetic Circular Dichroism At The Tb L3,2 Edges: Experiment Versus Theory, H. Wende, Z. Li, A. Scherz, G. Ceballos, K. Baberschke, A. Ankudinov, J. J. Rehr, F. Wilhelm, A. Rogalev, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

We investigate the x-ray magnetic circular dichroism (XMCD) at the L3,2 edges using a single crystal of Tb as a prototype system for a one-element magnet in order to ascertain the multipolar nature of the features in the dichroic spectra. The high resolution of the experimental data allows for a clear identification of the dipolar (E1: 2p→5d) and quadrupolar (E2: 2p→4f) transitions. On the basis of ab initio calculations we developed a simple procedure to extract the quadrupolar part by subtracting the derivative of the spin-averaged absorption spectra from the ...


Temperature And Stress Dependencies Of The Magnetic And Magnetostrictive Properties Of Fe0.81ga0.19, R. A. Kellogg, Alison B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso May 2002

Temperature And Stress Dependencies Of The Magnetic And Magnetostrictive Properties Of Fe0.81ga0.19, R. A. Kellogg, Alison B. Flatau, A. E. Clark, M. Wun-Fogle, Thomas A. Lograsso

Ames Laboratory Conference Papers, Posters, and Presentations

It was recently reported that the addition of nonmagnetic Ga increased the saturation magnetostriction (λ100) of Fe over tenfold while leaving the rhombohedral magnetostriction (λ111) almost unchanged. To determine the relationship between the magnetostriction and the magnetization we measured the temperature and stress dependence of both the magnetostriction and magnetization from −21 °C to +80 °C under compressive stresses ranging from 14.4 MPa to 87.1 MPa. For this study a single crystal rod of Fe0.81Ga0.19 was quenched from 800 °C into water to insure a nearly random distribution of Ga atoms ...


Magnetostriction Of Ternary Fe–Ga–X Alloys (X=Ni,Mo,Sn,Al), J. B. Restorff, M. Wun-Fogle, A. E. Clark, Thomas A. Lograsso, A. R. Ross, Deborah L. Schlagel May 2002

Magnetostriction Of Ternary Fe–Ga–X Alloys (X=Ni,Mo,Sn,Al), J. B. Restorff, M. Wun-Fogle, A. E. Clark, Thomas A. Lograsso, A. R. Ross, Deborah L. Schlagel

Ames Laboratory Publications

Investigations were made into the effect of small additions of Ni, Mo, Sn, as well as larger additions of Al on the magnetostriction of single crystal Fe100−xGax alloys (x≅13). The Fe–Ga and Fe–Al systems are seemingly unique among the Fe-based alloys in having very large magnetostrictions in spite of Ga and Al being nonmagnetic. In this paper, we show how additions of Ni, Mo, Sn, and Al affect λ100 and λ111 of the binary Fe–Ga alloys. We substituted small amounts of Ni into a binary Fe–Ga alloy in an ...


Temperature-Dependent Hc2 Anisotropy In Mgb2 As Inferred From Measurements On Polycrystals, Sergey L. Bud'ko, Paul C. Canfield May 2002

Temperature-Dependent Hc2 Anisotropy In Mgb2 As Inferred From Measurements On Polycrystals, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

We present data on temperature-dependent anisotropy of the upper critical field of MgB2 obtained from the analysis of measurements on high-purity, low-resistivity polycrystals. The anisotropy decreases in a monotonic fashion with increase of temperature.


Examination Of The Relationship Between The Parameters Of Barkhausen Effect Model And Microstructure Of Magnetic Materials, Chester C.H. Lo, S. J. Lee, L. C. Kerdus, David C. Jiles May 2002

Examination Of The Relationship Between The Parameters Of Barkhausen Effect Model And Microstructure Of Magnetic Materials, Chester C.H. Lo, S. J. Lee, L. C. Kerdus, David C. Jiles

Center for Nondestructive Evaluation Publications

A relationship between the parameters of a hysteretic-stochastic process model of the Barkhausen effect (BE) and the microstructural features of a series of ferritic/pearlitic steel samples has been identified. The root-mean-square values and pulse height distributions of the experimental and modeled BE signals showed similar dependence on the pearlite content. The correlation length parameter ξ of the model, which represents the range of interaction of domain walls with pinning sites, was found to obey ξ=AVfDf+BVpDp where Vf(Vp)and Df(Dp) are the volume fraction and grain size of ferrite (pearlite).


Transverse-Mass Dependence Of Two-Pion Correlations In Au+Au Collisions At Root(Nn)-N-S=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration May 2002

Transverse-Mass Dependence Of Two-Pion Correlations In Au+Au Collisions At Root(Nn)-N-S=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Two-pion correlations in roots(NN) = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at roots(NN) = 4.1 , 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R-out/R-side) is consistent with unity and independent of k(T) .


Measurement Of Single Electrons And Implications For Charm Production In Au+Au Collisions At Root(Nn)-N-S=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration May 2002

Measurement Of Single Electrons And Implications For Charm Production In Au+Au Collisions At Root(Nn)-N-S=130 Gev, K. Adcox, Sergey Belikov, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios Petridis, Marzia Rosati, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Transverse momentum spectra of electrons from Au+Au collisions at roots(NN) = 130 GeV have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal dN(e)/dy for p(T) > 0.8 GeV/c is 0.025 +/- 0.004(stat) +/- 0.010( syst) in central collisions, and the corresponding charm cross section is 380 +/- 60(stat) +/- 200(syst ) mu b per ...


Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene Apr 2002

Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene

Duane D. Johnson

In situ high-temperature (1165–1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of two-dimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two ⟨110⟩ step energies was found to be 0.72±0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.


From Atomistic Lattice-Gas Models For Surface Reactions To Hydrodynamic Reaction-Diffusion Equations, James W. Evans, Da-Jiang Liu, M. Tammaro Mar 2002

From Atomistic Lattice-Gas Models For Surface Reactions To Hydrodynamic Reaction-Diffusion Equations, James W. Evans, Da-Jiang Liu, M. Tammaro

Mathematics Publications

Atomistic lattice-gas models for surface reactions can accurately describe spatial correlations and ordering in chemisorbed layers due to adspecies interactions or due to limited mobility of some adspecies. The primary challenge in such modeling is to describe spatiotemporal behavior in the physically relevant “hydrodynamic” regime of rapid diffusion of (at least some) reactant adspecies. For such models, we discuss the development of exact reaction-diffusion equations (RDEs) describing mesoscale spatialpattern formation in surface reactions. Formulation and implementation of these RDEs requires detailed analysis of chemical diffusion in mixed reactant adlayers, as well as development of novel hybrid and parallel simulation techniques.


Overview Of Phenix Results From The First Rhic Run, W. A. Zajc, Sergey Belikov, Delwyn D. Bluhm, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios N. Petridis, Marzia Rosati, Harold D. Skank, G. A. Sleege, W. D. Thomas, F. K. Wohn, Et Al., Phenix Collaboration Feb 2002

Overview Of Phenix Results From The First Rhic Run, W. A. Zajc, Sergey Belikov, Delwyn D. Bluhm, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, Athanasios N. Petridis, Marzia Rosati, Harold D. Skank, G. A. Sleege, W. D. Thomas, F. K. Wohn, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Results from the PHENIX experiment for the first RHIC run with Au-Au collisions at roots(NN) = 130 GeV are presented. The systematic variation with centrality of charged particle multiplicity, transverse energy, elliptic flow, identified particle spectra and yield ratios, and production of charged particles and pi(0)'s at high transverse momenta are presented. Results on two-pion correlations and electron spectra are also provided, along with a discussion of plans for the second run at RHIC.


Review Of Nuclear Reactions At The Ags, Craig Ogilvie Feb 2002

Review Of Nuclear Reactions At The Ags, Craig Ogilvie

Physics and Astronomy Publications

No abstract provided.


First-Principles Theory Of The Temperature And Compositional Dependence Of Atomic Short-Range Order In Disordered Cu-Pd Alloys, R. V. Chepulskii, J. B. Staunton, Ezio Bruno, B. Ginatempo, Duane D. Johnson Feb 2002

First-Principles Theory Of The Temperature And Compositional Dependence Of Atomic Short-Range Order In Disordered Cu-Pd Alloys, R. V. Chepulskii, J. B. Staunton, Ezio Bruno, B. Ginatempo, Duane D. Johnson

Duane D. Johnson

We combine the first-principles, Korringa-Kohn-Rostoker coherent potential approximation based calculations of compositional fluctuations with a statistical mechanical ring approximation to study the temperature (T) and composition (c) dependence of the atomic short-range order (SRO) in disordered, face-centred cubic, Cu-Pd alloys. The fourfold splitting of SRO peaks around the equivalent X(0,1,0) points in reciprocal space is obtained in a wide T−c region. Such splitting is shown to be an “energy” effect caused by the absolute minima of the Fourier transform of the effective atomic interactions and related previously to the existence of nested sheets of the disordered ...


Lorentz Transmission Electron Microscopy And Magnetic Force Microscopy Characterization Of Nife/Al-Oxide/Co Films, Andrew C. C. Yu, Chester C.H. Lo, Amanda K. Petford-Long, David C. Jiles, Terunobu Miyazaki Jan 2002

Lorentz Transmission Electron Microscopy And Magnetic Force Microscopy Characterization Of Nife/Al-Oxide/Co Films, Andrew C. C. Yu, Chester C.H. Lo, Amanda K. Petford-Long, David C. Jiles, Terunobu Miyazaki

Materials Science and Engineering Publications

Magnetization reversal process of NiFe/Al-oxide/Co junction films was observed directly using Lorentztransmission electron microscopy (LTEM) and magnetic force microscopy(MFM).In situmagnetizing experiments performed in both LTEM and MFM were facilitated by a pair of electromagnets, which were mounted on the sample stages. A two-stage magnetization reversal process for the junction film was clearly observed in LTEM with NiFe magnetization reversed first via domain wall motion followed by Co magnetization reversal via moment rotation and domain wall motion. Reversal mechanism and domain characteristics of the NiFe and Co layers showed very distinctive features. The magnetization curve of ...


Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Ii. Multivariant Phase Transformations And Stress Space Analysis, Valery I. Levitas, Dean L. Preston Jan 2002

Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Ii. Multivariant Phase Transformations And Stress Space Analysis, Valery I. Levitas, Dean L. Preston

Valery I. Levitas

In this paper, the three-dimensional Landau model of austenite-martensite transformations constructed in Part I is generalized to include transformations between an arbitrary number of martensitic variants. The model can incorporate all temperature-dependent thermomechanical properties of both phases for arbitrary crystal symmetries, including higher-order elastic constants, and it correctly describes the characteristic features of stress-strain curves for shape-memory alloys and steels, namely, constant transformation strain tensors, constant or weakly temperature dependent stress hysteresis, and transformation at nonzero tangent moduli. Geometric representations of the conditions for phase equilibrium and phase transformations in six-dimensional stress space are developed. For the cubic-tetragonal phase transformation ...


Inclusive Gluon Production In Deep Inelastic Scattering At High Parton Density, Yuri V. Kovchegov, Kirill Tuchin Jan 2002

Inclusive Gluon Production In Deep Inelastic Scattering At High Parton Density, Yuri V. Kovchegov, Kirill Tuchin

Kirill Tuchin

We calculate the cross section of single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear. The expression we obtain for the inclusive gluon production cross section is generated by this nonlinear evolution. We analyze the rapidity distribution of the produced gluons as well as their transverse momentum spectrum given by the derived expression for the inclusive cross section. We propose an ansatz for the multiplicity distribution of gluons produced in nuclear collisions which ...