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Iowa State University

2007

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Articles 1 - 30 of 67

Full-Text Articles in Physics

Inhomogeneous Exclusion Processes With Extended Objects: The Effect Of Defect Locations, J. J. Dong, Beate Schmittmann, R. K. P. Zia Nov 2007

Inhomogeneous Exclusion Processes With Extended Objects: The Effect Of Defect Locations, J. J. Dong, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We study the effects of local inhomogeneities, i.e., slow sites of hopping rate q<1, in a totally asymmetric simple exclusion process for particles of size ℓ⩾1 (in units of the lattice spacing). We compare the simulation results of ℓ=1 and ℓ>1 and notice that the existence of local defects has qualitatively similar effects on the steady state. We focus on the stationary current as well as the density profiles. If there is only a single slow site in the system, we observe a significant dependence of the current on the location of the slow site for both ℓ=1 and ℓ>1 cases. When two slow sites are introduced, more intriguing phenomena emerge, e.g., dramatic decreases in the current when the two are close ...


Magnetic Behavior Of Rmn2+Xal10−X (R=La,Gd) Crystals, Athena S. Sefat, Bin Li, Sergey L. Bud'ko, Paul C. Canfield Nov 2007

Magnetic Behavior Of Rmn2+Xal10−X (R=La,Gd) Crystals, Athena S. Sefat, Bin Li, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

The crystallographic and magnetic properties of the solution grown RMn2+xAl10−x (R=Gd and La) crystals with tetragonal (P4∕nmm) structure are investigated. For these, single-crystal x-ray diffraction results have shown the preferential occupation of excess manganese on the aluminum 8i crystallographic site. Due to excess Mn, there is evidence of local-moment magnetism in LaMn2+xAl10−x and their random distribution is thought to be responsible for the magnetic correlations below ∼50K and the spin-glass behavior below ∼3K. For GdMn2+xAl10−x, the extra manganese influences temperature below which the sample enters into a state with a net ferromagnetic ...


Measurement Of Single Muons At Forward Rapidity In P+P Collisions At Root S=200 Gev And Implications For Charm Production, 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 Nov 2007

Measurement Of Single Muons At Forward Rapidity In P+P Collisions At Root S=200 Gev And Implications For Charm Production, 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

Muon production at forward rapidity (1.5 <=|eta|<= 1.8) has been measured by the PHENIX experiment over the transverse momentum range 1 <= p(T)<= 3 GeV/c in root s=200 GeV p+p collisions at the Relativistic Heavy Ion Collider. After statistically subtracting contributions from light hadron decays an excess remains which is attributed to the semileptonic decays of hadrons carrying heavy flavor, i.e. charm quarks or, at high p(T), bottom quarks. The resulting muon spectrum from heavy flavor decays is compared to PYTHIA and a next-to-leading-order perturbative QCD calculation. PYTHIA is used to determine the charm quark spectrum that would produce the observed muon excess. The corresponding differential cross section for charm quark production at forward rapidity is determined to be d sigma(c (c) over bar)/dy|(y=1.6)=0.243 +/- 0.013(stat.)+/- 0.105(data syst.)(-0.087)(+0.049)(PYTHIA syst.) mb.


Posterminaries: More Or Less Modern, Alexander H. King Nov 2007

Posterminaries: More Or Less Modern, Alexander H. King

Alexander H. King

It is yet another sign that I am aging. More and more often when young researchers hand me a written report of their research, I find myself criticizing their introductory section: “You need to start your literature survey with the original papers on this topic. Go and read…” followed by a citation to some classic of the learned literature.


Stability Issues For Gas-Liquid Flows In Bubble Columns, Deify Law, Francine Battaglia, Theodore J. Heindel Nov 2007

Stability Issues For Gas-Liquid Flows In Bubble Columns, Deify Law, Francine Battaglia, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

In the present work, gas-liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian-Eulerian ensemble-averaging method in a two dimensional Cartesian system. The time-averaged gas holdup simulations are compared to experimental measurements of a cylindrical bubble column performed by Rampure et al. [1]. Numerical predictions are presented for the time-averaged gas holdup at various axial heights as a function of radial position. The effects of grid resolution, bubble pressure model, and drag coefficient models on the numerical predictions are examined. The bubble pressure model is reported to account for bubble stability, thus providing physical solutions. The ...


Qualitative Observations Of Dense Particle Motion In A Vibration-Excited Granular Bed, Timothy B. Morgan, Theodore J. Heindel Nov 2007

Qualitative Observations Of Dense Particle Motion In A Vibration-Excited Granular Bed, Timothy B. Morgan, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

The Brazil nut effect is a classic phenomenon in which larger objects typically migrate to the top of a bed of smaller granular media when exposed to vibration. An example of this phenomenon is finding Brazil nuts on the top of a can of mixed nuts. In this study, the Brazil nut problem is simulated by submerging a large particle in a bed of granular media and then subjecting the system to vibration. Stereoscopic X-ray imaging is used to visualize the large particle motion. These images are then compiled into movies where the particle motion may be tracked. Observations of ...


Angular Dependence Of The Spin-Flop Transition And A Possible Structure Of The Spin-Flop Phase Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Oct 2007

Angular Dependence Of The Spin-Flop Transition And A Possible Structure Of The Spin-Flop Phase Of Gd5ge4, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The angular dependence of the spin-flop transition in Gd5Ge4 has been examined by magnetization measurements of a single crystal. When the magnetic field vector is tilted away from the antiferromagnetic easy axis (c axis) toward the b axis, the spin-flop transition always remains first order in nature. However, when the field vector is tilted away from the c axis toward the a axis, the first order spin-flop transition is only observed over a narrow range of tilt angles (0<θ<20°), which serves as evidence that the Gd moments “flop” from the c axis to the a axis during the spin-flop transformation.


Field Step Size And Temperature Effects On The Character Of The Magnetostructural Transformation In A Gd5ge4 Single Crystal, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso Oct 2007

Field Step Size And Temperature Effects On The Character Of The Magnetostructural Transformation In A Gd5ge4 Single Crystal, Zhong W. Ouyang, Vitalij K. Pecharsky, Karl A. Gschneidner Jr., Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

The critical magnetic fields required to induce the magnetostructural transformation below ∼30 K in Gd5Ge4 are dependent on the size of the magnetic-field step employed during isothermal measurements of magnetization: the smaller the step, the lower the critical field. The influence of the magnetic-field step size on the character of the magnetostructural transition in Gd5Ge4 diminishes as temperature increases, nearly disappearing above ∼30 K. Decreasing the size of the field step also leads to the formation of multiple steps in the magnetization. The steps are reproducible in the same sample at low temperatures (below ...


Spectrally Narrowed Edge Emission From Organic Light-Emitting Diodes, Yun Tian, Zhengqing Gan, Zhaoqun Zhou, David W. Lynch, Joseph Shinar, Ji-Hun Kang, Q-Han Park Oct 2007

Spectrally Narrowed Edge Emission From Organic Light-Emitting Diodes, Yun Tian, Zhengqing Gan, Zhaoqun Zhou, David W. Lynch, Joseph Shinar, Ji-Hun Kang, Q-Han Park

Physics and Astronomy Publications

A dramatic spectrally narrowed edge emission (SNEE) from small molecular organic light-emitting diodes at room temperature, with a full width at half maximum of 5–10nm, is described. The results show that this emission is due to irregular waveguide modes that leak from the indium tin oxide anode to the glass substrate at a grazing angle. Measurements of variable stripe length devices exhibit an apparent weak optical gain, but there is no observable threshold bias associated with this SNEE. Hence this apparent “optical gain” is suspected to result from misalignment of the propagating leaky waveguide mode and the collecting optics.


Field-Driven Structural Phase Transition And Sign-Switching Magnetocaloric Effect In Ni–Mn–Sn, M. Pasquale, C. P. Sasso, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel Sep 2007

Field-Driven Structural Phase Transition And Sign-Switching Magnetocaloric Effect In Ni–Mn–Sn, M. Pasquale, C. P. Sasso, L. Giudici, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

Depending on the starting equilibrium temperature, the application of a magnetic field on a sample of Ni–Mn–Sn produces sample heating or cooling during adiabatic experiments. The competition between endothermal and exothermal effects is observed close to the martensite-to-austenite magnetostructural phase transition. A model assuming the coexistence of two phases and a field dependence of their volume allows to compute the evolution of entropy and heat capacity during the phase transition. The correct fitting of the results suggests that the field-induced reduction of the martensite-to-austenite transition temperature is responsible for the observed sign switching of the magnetocaloric effect.


Detailed Study Of High-P(T) Neutral Pion Suppression And Azimuthal 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 Sep 2007

Detailed Study Of High-P(T) Neutral Pion Suppression And Azimuthal 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

Measurements of neutral pion (pi(0)) production at midrapidity in root s(NN)=200 GeV Au+Au collisions as a function of transverse momentum, p(T), collision centrality, and angle with respect to reaction plane are presented. The data represent the final pi(0) results from the PHENIX experiment for the first RHIC Au+Au run at design center-of-mass energy. They include additional data obtained using the PHENIX Level-2 trigger with more than a factor of 3 increase in statistics over previously published results for p(T)>6 GeV/c. We evaluate the suppression in the yield of high-p(T ...


Measurement Of Density Correlations In Pseudorapidity Via Charged Particle Multiplicity Fluctuations 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 Sep 2007

Measurement Of Density Correlations In Pseudorapidity Via Charged Particle Multiplicity Fluctuations 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

Longitudinal density correlations of produced matter in Au+Au collisions at root s(NN)=200 GeV have been measured from the inclusive charged particle distributions as a function of pseudorapidity window sizes. The extracted alpha xi parameter, related to the susceptibility of the density fluctuations in the long-wavelength limit, exhibits a nonmonotonic behavior as a function of the number of participant nucleons, N-part. A local maximum is seen at N-part similar to 90, with corresponding energy density based on the Bjorken picture of epsilon(Bj)tau similar to 2.4 GeV/(fm(2)c) with a transverse area size of ...


Inclusive Cross Section And Double Helicity Asymmetry For Pi(0) Production In P+P Collisions At Root S=200 Gev: Implications For The Polarized Gluon Distribution In The Proton, Andrew Adare, 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 2007

Inclusive Cross Section And Double Helicity Asymmetry For Pi(0) Production In P+P Collisions At Root S=200 Gev: Implications For The Polarized Gluon Distribution In The Proton, Andrew Adare, 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 experiment presents results from the Relativistic Heavy Ion Collider 2005 run with polarized proton collisions at root s=200 GeV, for inclusive pi(0) production at midrapidity. Unpolarized cross section results are given for transverse momenta p(T)=0.5 to 20 GeV/c, extending the range of published data to both lower and higher p(T). The cross section is described well for p(T)< 1 GeV/c by an exponential in p(T), and, for p(T)> 2 GeV/c, by perturbative QCD. Double helicity asymmetries A(LL) are presented based on a factor of 5 improvement in uncertainties as compared to previously published results, due to both an ...


Anomalous Phonon Behavior In The High-Temperature Shape-Memory Alloy Ti50pd50−Xcrx, S. M. Shapiro, Guangyong Xu, Deborah L. Schlagel, Thomas A. Lograsso, R. Erwin Aug 2007

Anomalous Phonon Behavior In The High-Temperature Shape-Memory Alloy Ti50pd50−Xcrx, S. M. Shapiro, Guangyong Xu, Deborah L. Schlagel, Thomas A. Lograsso, R. Erwin

Ames Laboratory Publications

Ti50Pd50−xCrx is a high-temperature shape-memory alloy with a martensitic transformation temperature strongly dependent on the Cr composition. Prior to the transformation, a premartensitic phase is present with an incommensurate modulated cubic lattice with wave vector of q0=(0.22,0.22,0). The temperature dependence of the diffuse scattering in the cubic phase is measured as a function temperature for x=6.5, 8.5, and 10 at. %. The lattice dynamics has been studied and reveals anomalous temperature andq dependences of the [110]-TA2 transverse phonon branch. The phonon linewidth is broad ...


Magnetic Phase Transition In The Itinerant Helimagnet Mnsi: Thermodynamic And Transport Properties, Sergei M. Stishov, Alla E. Petrova, S. Khasonov, G. Kh. Panova, Anatoly A. Shikov, Jason C. Lashley, D. Wu, Thomas A. Lograsso Aug 2007

Magnetic Phase Transition In The Itinerant Helimagnet Mnsi: Thermodynamic And Transport Properties, Sergei M. Stishov, Alla E. Petrova, S. Khasonov, G. Kh. Panova, Anatoly A. Shikov, Jason C. Lashley, D. Wu, Thomas A. Lograsso

Ames Laboratory Publications

A careful study of thermodynamic and transport properties of a high-quality single crystal of MnSi at ambient pressure suggests that its transition to a helical magnetic state near 29 K is weakly first order. The heat capacity, temperature derivative of resistivity, thermal expansion, and magnetic susceptibility exhibit a specific structure around the phase transition point, interpreted as a combination of first- and second-order features. Striking mirror symmetry between the temperature derivative of resistivity and the thermal expansion coefficient is observed. Conclusions drawn from these experiments question prevailing views on the phase diagram of MnSi.


Phenix Upgrade: Novel Stripixel Detector For Heavy Quark Detection And Proton Spin Structure Measurements At Rhic Energies, R. Nouicer, 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 2007

Phenix Upgrade: Novel Stripixel Detector For Heavy Quark Detection And Proton Spin Structure Measurements At Rhic Energies, R. Nouicer, 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

New design of silicon stripixel sensor has been developed at BNL for PHENIX upgrade. The sensor is a single-sided, DC-coupled, two-dimensional position sensitive device with good position resolution. This design is simpler for sensor fabrication and signal processing than the conventional double-sided strip sensor. HPK has produced pre-production stripixel sensors with thickness of 625 μm. The quality assurance tests show that the very low leakage current 0.12 nA per strip allows the use of the SVX4 chip. A long term stability test shows that the leakage current is stable over a long period of time. The study of the ...


Kinetic Monte Carlo Simulation Of Epitaxial Thin Film Growth: Formation Of Submonolayer Islands And Multilayer Mounds, James W. Evans, Patricia A. Thiel, Maozhi Li Aug 2007

Kinetic Monte Carlo Simulation Of Epitaxial Thin Film Growth: Formation Of Submonolayer Islands And Multilayer Mounds, James W. Evans, Patricia A. Thiel, Maozhi Li

Chemistry Conference Papers, Posters and Presentations

No abstract provided.


Power Spectra Of The Total Occupancy In The Totally Asymmetric Simple Exclusion Process, D. `A. Adams, R. K. P. Zia, Beate Schmittmann Jul 2007

Power Spectra Of The Total Occupancy In The Totally Asymmetric Simple Exclusion Process, D. `A. Adams, R. K. P. Zia, Beate Schmittmann

Beate Schmittmann

As a solvable and broadly applicable model system, the totally asymmetric exclusion process enjoys iconic status in the theory of nonequilibrium phase transitions. Here, we focus on the time dependence of the total number of particles on a 1-dimensional open lattice and its power spectrum. Using both Monte Carlo simulations and analytic methods, we explore its behavior in different characteristic regimes. In the maximal current phase and on the coexistence line (between high and low density phases), the power spectrum displays algebraic decay, with exponents −1.62 and −2.00, respectively. Deep within the high and low density phases, we ...


Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King Jul 2007

Control Of Porosity In Fluoride Thin Films Prepared By Vapor Deposition, Alexander H. King

Alexander H. King

We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF2), and calcium fluoride (CaF2) as a function of the substrate temperature for films deposited by thermal evaporation onto glass substrates. The amount of porosity in the thin films was measured using an atomic force microscope and a quartz crystal thickness monitor. The porosity was very sensitive to the substrate temperature and decreased as the substrate temperature increased. Consistent behavior was observed among all of the materials in this study.


Elliptic Flow For Phi Mesons And (Anti)Deuterons In Au+Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jul 2007

Elliptic Flow For Phi Mesons And (Anti)Deuterons In Au+Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Differential elliptic flow (v(2)) for phi mesons and (anti)deuterons ((d) over bar )d is measured for Au + Au collisions at root s(NN) = 200 GeV. The v(2) for phi mesons follows the trend of lighter pi(+/-) and K-+/- mesons, suggesting that ordinary hadrons interacting with standard hadronic cross sections are not the primary driver for elliptic flow development. The v(2) values for ((d) over bar )d suggest that elliptic flow is additive for composite particles. This further validation of the universal scaling of v(2) per constituent quark for baryons and mesons suggests that partonic collectivity ...


Visualizing Fluid Flows With X-Rays, Theodore J. Heindel, Terrence C. Jensen, Joseph N. Gray Jul 2007

Visualizing Fluid Flows With X-Rays, Theodore J. Heindel, Terrence C. Jensen, Joseph N. Gray

Mechanical Engineering Conference Presentations, Papers, and Proceedings

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will ...


Posterminaries: Full Circle, Alexander H. King Jul 2007

Posterminaries: Full Circle, Alexander H. King

Alexander H. King

A few years ago, I was walking near the old Union Station in Pittsburgh with a colleague only slightly younger than myself, when we happened upon some large-scale relics of the steel industry displayed for public viewing. “You don’t see too many of those in public parking lots,” I offered. “Um… what is it?” was the response. I suppose I was just a little surprised that a prominent materials scientist did not recognize a Bessemer converter—arguably the principal source of wealth during the U.S. industrial revolution—but this conversation took place back when steel was in decline ...


Controlling Surface Morphologies By Time-Delayed Feedback, M. Block, Beate Schmittmann, E. Schöll Jun 2007

Controlling Surface Morphologies By Time-Delayed Feedback, M. Block, Beate Schmittmann, E. Schöll

Beate Schmittmann

We propose a method to control the roughness of a growing surface via a time-delayed feedback scheme. The method is very general and can be applied to a wide range of nonequilibrium growth phenomena, from solid-state epitaxy to tumor growth. Possible experimental realizations are suggested. As an illustration, we consider the Kardar-Parisi-Zhang equation [Phys. Rev. Lett. 56, 889 (1986)] in 1+1 dimensions and show that the effective growth exponent of the surface width can be stabilized at any desired value in the interval [0.25, 0.33], for a significant length of time.


Correlated Production Of P And (P)Over-Bar In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jun 2007

Correlated Production Of P And (P)Over-Bar In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Correlations between p and (p) over bar at transverse momenta typical of enhanced baryon production in Au + Au collisions are reported. The PHENIX experiment has measured same and opposite sign baryon pairs in Au + Au collisions at root s(NN) = 200 GeV. Correlated production of p and p with the trigger particle from the range 2.5 < p(T) < 4.0 GeV/c and the associated particle with 1.8 < p(T) < 2.5 GeV/c is observed to be nearly independent of the centrality of the collisions. Same sign pairs show no correlation at any centrality. The conditional yield of mesons triggered by baryons (and anti-baryons) and mesons in the same p(T) range rises with increasing centrality, except for the most central collisions, where baryons show a significantly smaller number of associated mesons. These data are consistent with a picture in which hard scattered partons produce correlated p and (p) over bar in the p(T) region of the baryon excess.


Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson Jun 2007

Density Functional Study Of Structural Trends For Late-Transition-Metal 13-Atom Clusters, Lin-Lin Wang, Duane D. Johnson

Duane D. Johnson

Because reactivity increases as particle size decreases and competition between numerous structures are possible, which affects catalytic and magnetic properties, we study the structural trends of late-transition-metal 13-atom clusters using density functional theory within the generalized gradient approximation to exchange-correlation functional. We consider open structural motifs, such as bilayer and cubic (recently found to have lower energy), and find new bilayer candidates that are even lower in energy. To study the influence of d-orbital filling on structural trends, we focus on Pt, Pd, and Rh clusters and find several new, low-energy structures for Pt13 and Pd13 from searches using a ...


Generic Two-Phase Coexistence, Relaxation Kinetics, And Interface Propagation In The Quadratic Contact Process: Simulation Studies, Xiaofang Guo, Da-Jiang Liu, James W. Evans Jun 2007

Generic Two-Phase Coexistence, Relaxation Kinetics, And Interface Propagation In The Quadratic Contact Process: Simulation Studies, Xiaofang Guo, Da-Jiang Liu, James W. Evans

Physics and Astronomy Publications

The quadratic contact process is formulated as an adsorption-desorption model on a two-dimensional square lattice. It involves random adsorption at empty sites and correlated desorption requiring diagonally adjacent pairs of empty neighbors. We assess the model behavior utilizing kinetic Monte Carlo simulations. One finds generic two-phase coexistence between a low-coverage active steady state and a completely covered or "poisoned" absorbing steady state; i.e., both states are stable over a finite range of adsorption rates or "pressures." This behavior is in marked contrast to that for equilibrium phase separation. For spatially homogeneous systems, we provide a comprehensive characterization of the ...


System Size And Energy Dependence Of Jet-Induced Hadron Pair Correlation Shapes In Cu+Cu And Au+Au Collisions At Root S-Nn 200 And 62.4 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration Jun 2007

System Size And Energy Dependence Of Jet-Induced Hadron Pair Correlation Shapes In Cu+Cu And Au+Au Collisions At Root S-Nn 200 And 62.4 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, F. K. Wohn, X. Zong, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We present azimuthal angle correlations of intermediate transverse momentum (1-4 GeV/c) hadrons from dijets in Cu+Cu and Au+Au collisions at root s(NN)=62.4 and 200 GeV. The away-side dijet induced azimuthal correlation is broadened, non-Gaussian, and peaked away from Delta phi=pi in central and semicentral collisions in all the systems. The broadening and peak location are found to depend upon the number of participants in the collision, but not on the collision energy or beam nuclei. These results are consistent with sound or shock wave models, but pose challenges to Cherenkov gluon radiation models.


J/Psi Production Versus Centrality, Transverse Momentum, And Rapidity In Au+Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Jun 2007

J/Psi Production Versus Centrality, Transverse Momentum, And Rapidity In Au+Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Sergey Belikov, Paul Constantin, Nathan C. Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Jan Rak, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured J/psi production for rapidities -2.2 < y < 2.2 in Au+Au collisions at root s(NN)=200 GeV. The J/psi invariant yield and nuclear modification factor R-AA as a function of centrality, transverse momentum, and rapidity are reported. A suppression of J/psi relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy J/psi data at the CERN Super Proton Synchrotron invoking only J/psi destruction based on the local medium density predict a significantly larger suppression at RHIC and more suppression at midrapidity than at forward rapidity. Both trends are contradicted by our data.


J/Psi Production Versus Transverse Momentum And Rapidity In P+P Collisions At Root S=200 Gev, Andrew Adare, 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 Jun 2007

J/Psi Production Versus Transverse Momentum And Rapidity In P+P Collisions At Root S=200 Gev, Andrew Adare, 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

J/psi production in p+p collisions at root s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over a rapidity range of -2.2 < y < 2.2 and a transverse momentum range of 0 < p(T)< 9 GeV/c. The size of the present data set allows a detailed measurement of both the p(T) and the rapidity distributions and is sufficient to constrain production models. The total cross section times the branching ratio is B-ll sigma(J/psi)(pp)=178 +/- 3(stat)+/- 53(sys)+/- 18(norm) nb.


Irreversible Field Induced Magnetostriction At Temperatures Above And Below The Order-Disorder Transition In Single Crystal Tb5si2.2ge1.8, A. P. Ring, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles May 2007

Irreversible Field Induced Magnetostriction At Temperatures Above And Below The Order-Disorder Transition In Single Crystal Tb5si2.2ge1.8, A. P. Ring, Thomas A. Lograsso, Deborah L. Schlagel, J. E. Snyder, David C. Jiles

Ames Laboratory Conference Papers, Posters, and Presentations

This paper reports on the behavior of single crystal Tb5Si2.2Ge1.8 in the vicinity of its order-disorder and order-order phase transition from a higher temperature paramagnetic∕monoclinic state to a lower temperature ferromagnetic∕orthorhombic state. Measurements have been made of thermal and field induced changes in strain along the crystallographic a axis. The material exhibits large strains of up to 1500 ppm when a magnetic field is applied to it in its paramagnetic state but much smaller strains when a field is applied to it in its ferromagnetic state. These field induced strains are ...