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Iowa State University

2012

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Articles 1 - 30 of 78

Full-Text Articles in Physics

Hydrostatic And Uniaxial Pressure Dependence Of Superconducting Transition Temperature Of Kfe2as2 Single Crystals, Sergey L. Bud'ko, Yong Liu, Thomas A. Lograsso, Paul C. Canfield Dec 2012

Hydrostatic And Uniaxial Pressure Dependence Of Superconducting Transition Temperature Of Kfe2as2 Single Crystals, Sergey L. Bud'ko, Yong Liu, Thomas A. Lograsso, Paul C. Canfield

Ames Laboratory Publications

We present heat capacity, c-axis thermal expansion and pressure-dependent, low-field, temperature-dependent magnetization for pressures up to ∼12 kbar, data for KFe2As2 single crystals. Tc decreases under pressure with dTc/dP≈−0.10 K/kbar. The inferred uniaxial, c-axis, pressure derivative is positive, dTc/dpc≈0.11 K/kbar. The data are analyzed in comparison with those for overdoped Fe-based superconductors. Arguments are presented that superconductivity in KFe2As2 may be different from the other overdoped, Fe-based materials in the 122 family.


Cold-Nuclear-Matter Effects On Heavy-Quark Production In D+Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Dec 2012

Cold-Nuclear-Matter Effects On Heavy-Quark Production In D+Au Collisions At Root S-Nn=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in d + Au and p + p collisions at root S-NN = 200 GeV in the transverse-momentum range 0.85 <= p(T)(e) <= 8.5 GeV/c. In central d + Au collisions, the nuclear modification factor R-dA at 1.5 < p(T) < 5 GeV/c displays evidence of enhancement of these electrons, relative to those produced in p + p collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy D meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the pi(0) and heavy-flavor-electron nuclear modification factors R-AA.


J/Ψ Suppression At Forward Rapidity In Au+Au Collisions At √Snn=39 And 62.4 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al. Dec 2012

J/Ψ Suppression At Forward Rapidity In Au+Au Collisions At √Snn=39 And 62.4 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al.

Physics and Astronomy Publications

We present measurements of the J/ψ invariant yields in √sNN=39 and 62.4 GeV Au + Au collisions at forward rapidity (1.2<|y|<2.2). Invariant yields are presented as a function of both collision centrality and transverse momentum. Nuclear modifications are obtained for central relative to peripheral Au + Au collisions (RCP) and for various centrality selections in Au + Au relative to scaled p + p cross sections obtained from other measurements (RAA). The observed suppression patterns at 39 and 62.4 GeV are quite similar to those previously measured at 200 GeV. This similar suppression presents a challenge to theoretical models that contain various competing mechanisms with different energy dependencies, some of which cause suppression and others enhancement.


Nano-Cr-Film-Based Solar Selective Absorber With High Photo-Thermal Conversion Efficiency And Good Thermal Stability, Wei-Xi Zhou, Yan Shen, Er-Tao Hu, Yuan Zhao, Ming-Yu Sheng, Yu-Xiang Zheng, Song-You Wang, Young-Pak Lee, Cai-Zhuang Wang, David W. Lynch, Liang-Yao Chen Dec 2012

Nano-Cr-Film-Based Solar Selective Absorber With High Photo-Thermal Conversion Efficiency And Good Thermal Stability, Wei-Xi Zhou, Yan Shen, Er-Tao Hu, Yuan Zhao, Ming-Yu Sheng, Yu-Xiang Zheng, Song-You Wang, Young-Pak Lee, Cai-Zhuang Wang, David W. Lynch, Liang-Yao Chen

Physics and Astronomy Publications

Optical properties and thermal stability of the solar selective absorber based on the metal/dielectric four-layer film structure were investigated in the variable temperature region. Numerical calculations were performed to simulate the spectral properties of multilayer stacks with different metal materials and film thickness. The typical four-layer film structure using the transition metal Cr as the thin solar absorbing layer [SiO2(90nm)/Cr(10nm)/SiO2(80nm)/Al (≥100nm)] was fabricated on the Si or K9 glass substrate by using the magnetron sputtering method. The results indicate that the metal/dielectric film structure has a good spectral selective property ...


Epidemic Spreading On Preferred Degree Adaptive Networks, Shivakumar Jolad, Wenjia Liu, Beate Schmittmann, R. K. P. Zia Nov 2012

Epidemic Spreading On Preferred Degree Adaptive Networks, Shivakumar Jolad, Wenjia Liu, Beate Schmittmann, R. K. P. Zia

Physics and Astronomy Publications

We study the standard SIS model of epidemic spreading on networks where individuals have a fluctuating number of connections around a preferred degree . Using very simple rules for forming such preferred degree networks, we find some unusual statistical properties not found in familiar Erdös-Rényi or scale free networks. By letting depend on the fraction of infected individuals, we model the behavioral changes in response to how the extent of the epidemic is perceived. In our models, the behavioral adaptations can be either ‘blind’ or ‘selective’ – depending on whether a node adapts by cutting or adding links to randomly chosen partners ...


Cross Sections And Double-Helicity Asymmetries Of Midrapidity Inclusive Charged Hadrons In P Plus P Collisions At Root S = 62.4 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Nov 2012

Cross Sections And Double-Helicity Asymmetries Of Midrapidity Inclusive Charged Hadrons In P Plus P Collisions At Root S = 62.4 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Unpolarized cross sections and double-helicity asymmetries of single-inclusive positive and negative charged hadrons at midrapidity from p + p collisions at root s = 62.4 GeV are presented. The PHENIX measurement of the cross sections for 1.0 < p(T) < 4.5 GeV/c are consistent with perturbative QCD calculations at next-to-leading order in the strong-coupling constant, alpha(s). Resummed pQCD calculations including terms with next-to-leading-log accuracy, yielding reduced theoretical uncertainties, also agree with the data. The double-helicity asymmetry, sensitive at leading order to the gluon polarization in a momentum-fraction range of 0.05 less than or similar to x(gluon) less than or similar to 0.2, is consistent with recent global parametrizations disfavoring large gluon polarization.


Direct Photon Production In P Plus P Collisions At Root S=200 Gev At Midrapidity, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Oct 2012

Direct Photon Production In P Plus P Collisions At Root S=200 Gev At Midrapidity, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The differential cross section for the production of direct photons in p + p collisions at root s = 200 GeV at midrapidity was measured in the PHENIX detector at the Relativistic Heavy Ion Collider. Inclusive direct photons were measured in the transverse momentum range from 5: 5-25 GeV/c, extending the range beyond previous measurements. Event structure was studied with an isolation criterion. Next-to-leading-order perturbative-quantum-chromodynamics calculations give a good description of the spectrum. When the cross section is expressed versus x(T), the PHENIX data are seen to be in agreement with measurements from other experiments at different center-of-mass energies.


Effects Of Transition Metal Substitutions On The Incommensurability And Spin Fluctuations In Bafe2as2 By Elastic And Inelastic Neutron Scattering, Min Gyu Kim, Jagat Lamsal, T. W. Heitmann, Gregory S. Tucker, Daniel K. Pratt, Suffian N. Khan, Y. B. Lee, Aftab Alam, Alexander N. Thaler, Ni Ni, Sheng Ran, Sergey L. Bud'ko, K. J. Marty, M. D. Lumsden, Paul C. Canfield, Bruce N. Harmon, Duane D. Johnson, Andreas Kreyssig, Robert J. Mcqueeney, Alan I. Goldman Oct 2012

Effects Of Transition Metal Substitutions On The Incommensurability And Spin Fluctuations In Bafe2as2 By Elastic And Inelastic Neutron Scattering, Min Gyu Kim, Jagat Lamsal, T. W. Heitmann, Gregory S. Tucker, Daniel K. Pratt, Suffian N. Khan, Y. B. Lee, Aftab Alam, Alexander N. Thaler, Ni Ni, Sheng Ran, Sergey L. Bud'ko, K. J. Marty, M. D. Lumsden, Paul C. Canfield, Bruce N. Harmon, Duane D. Johnson, Andreas Kreyssig, Robert J. Mcqueeney, Alan I. Goldman

Ames Laboratory Publications

The spin fluctuation spectra from nonsuperconducting Cu-substituted, and superconducting Co-substituted, BaFe2As2 are compared quantitatively by inelastic neutron scattering measurements and are found to be indistinguishable. Whereas diffraction studies show the appearance of incommensurate spin-density wave order in Co and Ni substituted samples, the magnetic phase diagram for Cu substitution does not display incommensurate order, demonstrating that simple electron counting based on rigid-band concepts is invalid. These results, supported by theoretical calculations, suggest that substitutional impurity effects in the Fe plane play a significant role in controlling magnetism and the appearance of superconductivity, with Cu distinguished by enhanced impurity scattering and ...


Weak Anti-Localization And Quantum Oscillations Of Surface States In Topological Insulator Bi2se2te, Lihong Bao, Liang He, Nicholas R. Meyer, Xufeng Kou, Peng Zhang, Zhi-Gang Chen, Alexei V. Fedorov, Trevor M. Riedemann, Thomas A. Lograsso, Kang L. Wang, Gary Tuttle, Faxian Xiu Oct 2012

Weak Anti-Localization And Quantum Oscillations Of Surface States In Topological Insulator Bi2se2te, Lihong Bao, Liang He, Nicholas R. Meyer, Xufeng Kou, Peng Zhang, Zhi-Gang Chen, Alexei V. Fedorov, Trevor M. Riedemann, Thomas A. Lograsso, Kang L. Wang, Gary Tuttle, Faxian Xiu

Ames Laboratory Publications

Topological insulators, a new quantum state of matter, create exciting opportunities for studying topological quantum physics and for exploring spintronic applications due to their gapless helical metallic surface states. Here, we report the observation of weak anti-localization and quantum oscillations originated from surface states in Bi2Se2Te crystals. Angle-resolved photoemission spectroscopy measurements on cleaved Bi2Se2Te crystals show a well-defined linear dispersion without intersection of the conduction band. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model and the extracted phase coherent length shows a power-law dependence with temperature ( ∼T−0.44), indicating the presence of the surface states. More ...


Evolution Of Pi(0) Suppression In Au Plus Au Collisions From Root S(Nn)=39 To 200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration Oct 2012

Evolution Of Pi(0) Suppression In Au Plus Au Collisions From Root S(Nn)=39 To 200 Gev, Andrew Adare, Lei Ding, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, C. L. Silva, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Neutral-pion pi(0) spectra were measured at midrapidity (vertical bar y vertical bar < 0.35) in Au + Au collisions at root s(NN) = 39 and 62.4 GeV and compared with earlier measurements at 200 GeV in a transverse-momentum range of 1 < p(T) < 10 GeV/c. The high-p(T) tail is well described by a power law in all cases, and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding spectra for p + p collisions. The nuclear modification factors (RAA) show significant suppression, with a distinct energy, centrality, and p(T) dependence. Above p(T) = 7 GeV/c, R-AA is similar for root sNN = 62.4 and 200 GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe R-AA well at 200 GeV fail to describe the 39 GeV data, raising the possibility that, for the same p(T) region, the relative importance of initial-state effects and soft processes increases at lower energies. The p(T) range where pi(0) spectra in central Au + Au collisions have the same power as in p + p collisions is approximate to 5 and 7 GeV/c for root sNN = 200 and 62.4 GeV, respectively. For the root sNN = 39 GeV data, it is not clear whether such a region is reached, and the x(T) dependence of the x(T)-scaling power-law exponent is very different from that observed in the root sNN = 62 and 200 GeV data, providing further evidence that initial-state effects and soft processes mask the in-medium suppression of hardscattered partons to higher p(T) as the collision energy decreases.


Measurement Of Direct Photons In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan Conrad 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 Oct 2012

Measurement Of Direct Photons In Au Plus Au Collisions At Root S(Nn)=200 Gev, S. Afanasiev, Sergey Belikov, Paul Constantin, Nathan Conrad 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

We report the measurement of direct photons at midrapidity in Au + Au collisions at root s(NN) = 200 GeV. The direct photon signal was extracted for the transverse momentum range of 4 GeV/c < pT < 22 GeV/c, using a statistical method to subtract decay photons from the inclusive photon sample. The direct photon nuclear modification factor R-AA was calculated as a function of p(T) for different Au + Au collision centralities using the measured p + p direct photon spectrum and compared to theoretical predictions. R-AA was found to be consistent with unity for all centralities over the entire measured pT range. Theoretical models that account for modifications of initial direct photon production due to modified parton distribution functions in Au and the different isospin composition of the nuclei predict a modest change of R-AA from unity. They are consistent with the data. Models with compensating effects of the quark-gluon plasma on high-energy photons, such as suppression of jet-fragmentation photons and induced-photon bremsstrahlung from partons traversing the medium, are also consistent with this measurement.


Structural And Functional Analysis Of The Transcriptional Regulator Rv3066 Of Mycobacterium Tuberculosis, Jani Reddy Bolla, Sylvia V. Do, Feng Long, Lei Dai, Chih-Chia Su, Hsiang-Ting Lei, Xiao Chen, Jillian E. Gerkey, Daniel C. Murphy, Kanagalaghatta R. Rajashankar, Qijing Zhang, Edward W. Yu Oct 2012

Structural And Functional Analysis Of The Transcriptional Regulator Rv3066 Of Mycobacterium Tuberculosis, Jani Reddy Bolla, Sylvia V. Do, Feng Long, Lei Dai, Chih-Chia Su, Hsiang-Ting Lei, Xiao Chen, Jillian E. Gerkey, Daniel C. Murphy, Kanagalaghatta R. Rajashankar, Qijing Zhang, Edward W. Yu

Veterinary Microbiology and Preventive Medicine Publications

The Mmr multidrug efflux pump recognizes and actively extrudes a broad range of antimicrobial agents, and promotes the intrinsic resistance to these antimicrobials in Mycobacterium tuberculosis . The expression of Mmr is controlled by the TetR-like transcriptional regulator Rv3066, whose open reading frame is located downstream of the mmr operon. To understand the structural basis of Rv3066 regulation, we have determined the crystal structures of Rv3066, both in the absence and presence of bound ethidium, revealing an asymmetric homodimeric two-domain molecule with an entirely helical architecture. The structures underscore the flexibility and plasticity of the regulator essential for multidrug recognition. Comparison ...


Evolution Of Precipitate Morphology During Heat Treatment And Its Implications For The Superconductivity In Kxfe1.6+Yse2 Single Crystals, Yong Liu, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso Oct 2012

Evolution Of Precipitate Morphology During Heat Treatment And Its Implications For The Superconductivity In Kxfe1.6+Yse2 Single Crystals, Yong Liu, Qingfeng Xing, Kevin W. Dennis, R. William Mccallum, Thomas A. Lograsso

Ames Laboratory Publications

We study the relationship between precipitate morphology and superconductivity in KxFe1.6+ySe2 single crystals grown by self-flux method. Scanning electron microscopy (SEM) measurements revealed that the superconducting phase forms a network in the samples quenched above iron vacancy order-disorder transition temperature Ts, whereas it aggregates into micrometer-sized rectangular bars and aligns as disconnected chains in the furnace-cooled samples. Accompanying this change in morphology the superconducting shielding fraction is strongly reduced. By post-annealing above Ts followed by quenching in room temperature water, the network recovers with a superconducting shielding fraction approaching 80% for ...


Observation Of Direct-Photon Collective Flow In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Sep 2012

Observation Of Direct-Photon Collective Flow In Au Plus Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au collisions at root s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p(T) > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with ...


Reply To “Comment On ‘Accurate And Fast Numerical Solution Of Poisson's Equation For Arbitrary, Space-Filling Voronoi Polyhedra: Near-Field Corrections Revisited’ ”, Aftab Alam, Brian G. Wilson, Duane D. Johnson Sep 2012

Reply To “Comment On ‘Accurate And Fast Numerical Solution Of Poisson's Equation For Arbitrary, Space-Filling Voronoi Polyhedra: Near-Field Corrections Revisited’ ”, Aftab Alam, Brian G. Wilson, Duane D. Johnson

Ames Laboratory Publications

This is a Reply to the Comment by Gonis and Zhang on our recent paper. They discuss supposed issues with our “accurate and fast numerical solution of Poisson’s equation for arbitrary Voronoi polyhedra” (VP).


Perturbation Theory Of Solid-Liquid Interfacial Free Energies Of Bcc Metals, Vadim B. Warshavsky, Xueyu Song Sep 2012

Perturbation Theory Of Solid-Liquid Interfacial Free Energies Of Bcc Metals, Vadim B. Warshavsky, Xueyu Song

Ames Laboratory Publications

A perturbation theory is used to calculate bcc solid-liquid interfacial free energies of metallic systems with embedded-atom model potentials. As a reference system for bcc crystals we used a single-occupancy cell, hard-sphere bcc system. Good agreements between the perturbation theory results and the corresponding results from simulations are found. The strategy to extract hard-sphere bcc solid-liquid interfacial free energies may have broader applications for other crystal lattices.


Cross-Imaging System Comparison Of Backscatter Coefficient Estimates From A Tissue-Mimicking Material, Kibo Nam, Ivan M. Rosado-Mendez, Lauren A. Wirtzfeld, Viksit Kumar, Ernest L. Madsen, Goutam Ghoshal, Alexander D. Pawlicki, Michael L. Oelze, Roberto J. Lavarello, Timothy A. Bigelow, James A. Zagzebski, William D. O'Brien Jr., Timothy J. Hall Sep 2012

Cross-Imaging System Comparison Of Backscatter Coefficient Estimates From A Tissue-Mimicking Material, Kibo Nam, Ivan M. Rosado-Mendez, Lauren A. Wirtzfeld, Viksit Kumar, Ernest L. Madsen, Goutam Ghoshal, Alexander D. Pawlicki, Michael L. Oelze, Roberto J. Lavarello, Timothy A. Bigelow, James A. Zagzebski, William D. O'Brien Jr., Timothy J. Hall

Electrical and Computer Engineering Publications

A key step toward implementing quantitative ultrasound techniques in a clinical setting is demonstrating that parameters such as the ultrasonic backscatter coefficient (BSC) can be accurately estimated independent of the clinical imaging system used. In previous studies, agreement in BSC estimates for well characterized phantoms was demonstrated across different laboratory systems. The goal of this study was to compare the BSC estimates of a tissue mimicking sample measured using four clinical scanners, each providing RF echo data in the 1-15 MHz frequency range. The sample was previously described and characterized with single-element transducer systems. Using a reference phantom for analysis ...


High Superconducting Anisotropy And Weak Vortex Pinning In Co-Doped Lafeaso, G. Li, G. Grissonnanche, J.-Q. Yan, R. William Mccallum, Thomas A. Lograsso, H. D. Zhou, L. Balicas Aug 2012

High Superconducting Anisotropy And Weak Vortex Pinning In Co-Doped Lafeaso, G. Li, G. Grissonnanche, J.-Q. Yan, R. William Mccallum, Thomas A. Lograsso, H. D. Zhou, L. Balicas

Ames Laboratory Publications

Here, we present an electrical transport study in single crystals of LaFe0.92Co0.08AsO (Tc≃9.1 K) under high magnetic fields. In contrast to most of the previously reported Fe based superconductors, and despite its relatively low Tc, LaFe0.92Co0.08AsO shows a superconducting anisotropy which is comparable to those seen, for instance, in the cuprates or γH=Hc2ab/Hc2c=mc/mab≃9, where mc/mab is the effective-mass anisotropy, although, in the present case and as in all Fe ...


Nuclear-Modification Factor For Open-Heavy-Flavor Production At Forward Rapidity In Cu Plus Cu Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nathan Conrad Grau, John C. Hill, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, S. Skutnik, Carla Vale, Et Al., Phenix Collaboration Aug 2012

Nuclear-Modification Factor For Open-Heavy-Flavor Production At Forward Rapidity In Cu Plus Cu Collisions At Root S(Nn)=200 Gev, Andrew Adare, Nathan Conrad 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

Background: Heavy-flavor production in p + p collisions is a good test of perturbative-quantum-chromodynamics (pQCD) calculations. Modification of heavy-flavor production in heavy-ion collisions relative to binary-collision scaling from p + p results, quantified with the nuclear-modification factor (R-AA), provides information on both cold-and hot-nuclear-matter effects. Midrapidity heavy-flavor R-AA measurements at the Relativistic Heavy Ion Collider have challenged parton-energy-loss models and resulted in upper limits on the viscosity-entropy ratio that are near the quantum lower bound. Such measurements have not been made in the forward-rapidity region.

Purpose: Determine transverse-momentum (p(T)) spectra and the corresponding R-AA for muons from heavy-flavor meson decay in ...


Reversible Tuning Of The Surface State In A Pseudobinary Bi2(Te-Se)3 Topological Insulator, Rui Jiang, Lin-Lin Wang, Mianliang Huang, R. S. Dhaka, Duane D. Johnson, Thomas A. Lograsso, Adam Kaminski Aug 2012

Reversible Tuning Of The Surface State In A Pseudobinary Bi2(Te-Se)3 Topological Insulator, Rui Jiang, Lin-Lin Wang, Mianliang Huang, R. S. Dhaka, Duane D. Johnson, Thomas A. Lograsso, Adam Kaminski

Ames Laboratory Publications

We use angle-resolved photoemission spectroscopy to study a nontrivial surface state in a pseudobinary Bi2Te2.8Se0.2 topological insulator. We show that, unlike previously studied binaries, this is an intrinsic topological insulator with the conduction bulk band residing well above the chemical potential. Our data indicate that under a good vacuum condition there are no significant aging effects for more than two weeks after cleaving. We also demonstrate that the shift of the Kramers point at low temperature is caused by UV-assisted absorption of molecular hydrogen. Our findings pave the way for applications of these ...


Directed Assembly Of Ru Nanoclusters On Ru(0001)-Supported Graphene: Stm Studies And Atomistic Modeling, Albert K. Engstfeld, Harry E. Hoster, R. Juergen Behm, Lyle D. Roelofs, Xiaojie Liu, Cai-Zhuang Wang, Yong Han, James W. Evans Aug 2012

Directed Assembly Of Ru Nanoclusters On Ru(0001)-Supported Graphene: Stm Studies And Atomistic Modeling, Albert K. Engstfeld, Harry E. Hoster, R. Juergen Behm, Lyle D. Roelofs, Xiaojie Liu, Cai-Zhuang Wang, Yong Han, James W. Evans

Physics and Astronomy Publications

Directed assembly of an array of Ru nanoclusters (NCs) is achieved by deposition of Ru at around room temperature on a single layer of graphene supported on Ru(0001). In this system, directed assembly is guided by the periodic moir´e structure of the buckled graphene sheet. Behavior is analyzed utilizing both scanning tunneling microscopy and atomistic lattice-gas modeling together with kinetic Monte Carlo simulation. We elucidate the kinetics of NC nucleation and growth, specifically assessing the coverage dependence of the NC density and height distribution. In addition, we provide a detailed characterization of the development of short-range spatial order ...


Creating Nanoscale Ag Patterns On The Si(111)–(√3 × √3)R30°-Ag Surface Via Guided Self-Assembly, Alex Belianinov, Barış Ünal, Michael C. Tringides, Patricia A. Thiel Jul 2012

Creating Nanoscale Ag Patterns On The Si(111)–(√3 × √3)R30°-Ag Surface Via Guided Self-Assembly, Alex Belianinov, Barış Ünal, Michael C. Tringides, Patricia A. Thiel

Chemistry Publications

Patterns of Ag nanostructures can be created on the Si(111)–(√3 × √3)R30°-Ag surface, using a simple two-step process in ultrahigh vacuum. First, patterns are created using the tip of a scanning tunneling microscope. Second, Ag is deposited at room temperature. The Ag diffuses over long distances on the surface and selectively aggregates at the patterned regions. The size of the Ag features is ∼3–4 nm.


Nanoalloy Composition-Temperature Phase Diagram For Catalyst Design: Case Study Of Ag-Au, Lin-Lin Wang, Teck L. Tan, Duane D. Johnson Jul 2012

Nanoalloy Composition-Temperature Phase Diagram For Catalyst Design: Case Study Of Ag-Au, Lin-Lin Wang, Teck L. Tan, Duane D. Johnson

Ames Laboratory Publications

By coupling a cluster expansion with density functional theory (DFT) calculations, we determine the configurational thermodynamics (site preferences and occupations) for alloyed nanoparticles (NPs) as functions of composition (c) and temperature (T), exemplified using a 55-atom Ag-Au truncated cuboctahedron NP. The c−T phase diagram for site occupations gives detailed design information for alloyed NP, especially the thermodynamically stable active sites for catalysis and how they change with stoichiometry and processing temperature. Generally, Ag prefers core and Au prefers shell, agreeing with our universal core-shell preference assessed from DFT impurity segregation energies but with interesting multishell configurations having specific active ...


Effects Of Cold Work On Near-Surface Conductivity Profiles In Laser Shock Peened And Shot Peened Nickel-Base Superalloy, Tyler J. Lesthaeghe, Brian F. Larson, Ramya Chandrasekar, Anatoli M. Frishman, Chester C.H. Lo, Norio Nakagawa Jul 2012

Effects Of Cold Work On Near-Surface Conductivity Profiles In Laser Shock Peened And Shot Peened Nickel-Base Superalloy, Tyler J. Lesthaeghe, Brian F. Larson, Ramya Chandrasekar, Anatoli M. Frishman, Chester C.H. Lo, Norio Nakagawa

Center for Nondestructive Evaluation Conference Papers, Posters and Presentations

This paper reports on a study of the effects of cold work induced by surface enhancement treatment on conductivity profiles in nickel-base superalloys, as part of the on-going efforts aimed at evaluating the feasibility of characterizing near-surface residual stress profiles in peened engine components using a swept frequency eddy current (SFEC) technique. The approach is based on the empirical piezoresistivity effect that correlates conductivity changes with residual stress, but recent studies have shown that conductivity changes induced by peening processes are also influenced by metallurgical factors such as cold work. In this study, conductivity deviation profiles were obtained by model-based ...


Acoustic Field Effects On Minimum Fluidization Velocity In A 3d Fluidized Bed, David R. Escudero, Theodore J. Heindel Jul 2012

Acoustic Field Effects On Minimum Fluidization Velocity In A 3d Fluidized Bed, David R. Escudero, Theodore J. Heindel

Mechanical Engineering Conference Presentations, Papers, and Proceedings

Fluidized beds are used in a variety of process industries because they provide uniform temperature distributions, low pressure drops, and high heat/mass rates. Minimum fluidization velocity is an important factor in understanding the hydrodynamic behavior of fluidized beds, and this characteristic may be modified through high frequency (sound) vibrations. The effects caused by sound wave frequency on the minimum fluidization velocity in a 3D fluidized bed are investigated in this study. Experiments are carried out in a 10.2 cm ID cold flow fluidized bed filled with glass beads with material density of 2600 kg/m3, and particles ...


X-Ray Diffuse Scattering Measurements Of Chemical Short-Range Order And Lattice Strains In A Highly Magnetostrictive Fe0.813ga0.187 Alloy In An Applied Magnetic Field, Yingzhou Du, Mianliang Huang, Thomas A. Lograsso, Robert J. Mcqueeney Jun 2012

X-Ray Diffuse Scattering Measurements Of Chemical Short-Range Order And Lattice Strains In A Highly Magnetostrictive Fe0.813ga0.187 Alloy In An Applied Magnetic Field, Yingzhou Du, Mianliang Huang, Thomas A. Lograsso, Robert J. Mcqueeney

Ames Laboratory Publications

The rapid growth of the magnetostriction coefficient of ferromagnetic Fe1−xGax alloys that occurs at a composition range from 0


Deviation From Quark Number Scaling Of The Anisotropy Parameter V(2) Of Pions, Kaons, And Protons In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration Jun 2012

Deviation From Quark Number Scaling Of The Anisotropy Parameter V(2) Of Pions, Kaons, And Protons In Au+Au Collisions At Root S(Nn)=200 Gev, Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

Measurements of the anisotropy parameter v(2) of identified hadrons (pions, kaons, and protons) as a function of centrality, transverse momentum p(T), and transverse kinetic energy KET at midrapidity (vertical bar eta vertical bar < 0.35) in Au + Au collisions at root s(N N) = 200 GeV are presented. Pions and protons are identified up to p(T) = 6 GeV/c, and kaons up to p(T) = 4 GeV/c, by combining information from time-of-flight and aerogel Cerenkov detectors in the PHENIX Experiment. The scaling of v(2) with the number of valence quarks (n(q)) has been studied in different centrality bins as a function of transverse momentum and transverse kinetic energy. A deviation from previously observed quark-number scaling is observed at large values of KET/n(q) in noncentral Au + Au collisions (20-60%), but this scaling remains valid in central collisions (0-10%).


Photonic Crystal: Energy-Related Applications, Zhuo Ye, Joong Mok Park, Kristen P. Constant, Tae Guen Kim, Kai-Ming Ho Jun 2012

Photonic Crystal: Energy-Related Applications, Zhuo Ye, Joong Mok Park, Kristen P. Constant, Tae Guen Kim, Kai-Ming Ho

Materials Science and Engineering Publications

We review recent work on photonic-crystal fabrication using soft-lithography techniques. We consider applications of the resulting structures in energy-related areas such as lighting and solar-energy harvesting. In general, our aim is to introduce the reader to the concepts of photonic crystals, describe their history, development, and fabrication techniques and discuss a selection of energy-related applications.


Generalized Hydrodynamic Treatment Of The Interplay Between Restricted Transport And Catalytic Reactions In Nanoporous Materials, David M. Ackerman, Jing Wang, James W. Evans Jun 2012

Generalized Hydrodynamic Treatment Of The Interplay Between Restricted Transport And Catalytic Reactions In Nanoporous Materials, David M. Ackerman, Jing Wang, James W. Evans

Physics and Astronomy Publications

Behavior of catalytic reactions in narrow pores is controlled by a delicate interplay between fluctuations in adsorption-desorption at pore openings, restricted diffusion, and reaction. This behavior is captured by a generalized hydrodynamic formulation of appropriate reaction-diffusion equations (RDE). These RDE incorporate an unconventional description of chemical diffusion in mixed-component quasi-single-file systems based on a refined picture of tracer diffusion for finite-length pores. The RDE elucidate the nonexponential decay of the steady-state reactant concentration into the pore and the non-mean-field scaling of the reactant penetration depth.


Ground And Excited State Charmonium Production In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration May 2012

Ground And Excited State Charmonium Production In P Plus P Collisions At Root S=200 Gev, Andrew Adare, Alan Dion, John C. Hill, Todd Kempel, John G. Lajoie, Alexandre Lebedev, Craig Ogilvie, H. Pei, Marzia Rosati, Alexey Yu. Semenov, C. L. Silva, Carla Vale, Feng Wei, Et Al., Phenix Collaboration

Physics and Astronomy Publications

We report on charmonium measurements [J/psi (1S), psi' (2S), and chi(c) (1P)] in p + p collisions at root s = 200 GeV. We find that the fraction of J/psi coming from the feed-down decay of psi' and chi(c) in the midrapidity region (vertical bar y vertical bar < 0: 35) is 9.6 +/- 2.4% and 32 +/- 9%, respectively. We also present the p(T) and rapidity dependencies of the J/psi yield measured via dielectron decay at midrapidity (vertical bar y vertical bar < 0.35) and via dimuon decay at forward rapidity (1.2 < vertical bar y vertical bar < 2.2). The statistical precision greatly exceeds that reported in our previous publication [Phys. Rev. Lett. 98, 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.