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2nd Workshop on Visual Performance analysis, VPA 2015

作者： Von Rüden, Laura Hermanns, Marc-André Behrisch, Michael Keim, Daniel Mohr, Bernd Wolf, Felix GSC Computational Engineering Parallel Programming TU Darmstadt Germany JARA-HPC RWTH Aachen University Germany Data Analysis and Visualization University of Konstanz Germany Jülich Supercomputing Centre Forschungszentrum Jülich Germany

ISBN: (纸本)9781450340137

Performance-analysis tools are indispensable for understanding and optimizing the behavior of parallel programs running on increasingly powerful supercomputers. However, with size and complexity of hardware and software on the rise, performance data sets are becoming so voluminous that their analysis poses serious challenges. In particular, the search space that must be traversed and the number of individual performance views that must be explored to identify phenomena of interest becomes too large. To mitigate this problem, we use visual analytics. Specifically, we accelerate the analysis of performance profiles by automatically identifying (1) relevant and (2) similar data subsets and their performance views. We focus on views of the virtual-process topology, showing that their relevance can be well captured with visual-quality metrics and that they can be further assigned to topical groups according to their visual features. A case study demonstrates that our approach helps reduce the search space by up to 80%. Copyright 2015 ACM.

关键词： Supercomputers

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Excitations in the field-induced quantum spin liquid state of α-RuCl3

arXiv

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arXiv 2017年

作者： Banerjee, A. Lampen-Kelley, P. Knolle, J. Balz, C. Aczel, A.A. Winn, B. Liu, Y. Pajerowski, D. Yan, J.-Q. Bridges, C.A. Savici, A.T. Chakoumakos, B.C. Lumsden, M.D. Tennant, D.A. Moessner, R. Mandrus, D.G. Nagler, S.E. Quantum Condensed Matter Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Department of Materials Science and Engineering University of Tennessee KnoxvilleTN37996 United States Department of Physics Cavendish Laboratory JJ Thomson Avenue CambridgeCB3 0HE United Kingdom Chemical Sciences Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Neutron Sciences Directorate Oak Ridge National Laboratory Oak RidgeTN37831 United States Max Planck Institute for the Physics of Complex Systems DresdenD-01187 Germany

The Kitaev model on a honeycomb lattice predicts a paradigmatic quantum spin liquid (QSL) exhibiting Majorana Fermion excitations. The insight that Kitaev physics might be realized in practice has stimulated investigations of candidate materials, recently including α-RuCl3. In all the systems studied to date, significant non-Kitaev interactions induce magnetic order at low temperature. However, in-plane magnetic fields of roughly 8 Tesla suppress the long-range magnetic order in α-RuCl3 raising the intriguing possibility of a field-induced QSL exhibiting non-Abelian quasiparticle excitations. Here we present inelastic neutron scattering in αRuCl3 in an applied magnetic field. At a field of 8 Tesla the spin waves characteristic of the ordered state vanish throughout the Brillouin zone. The remaining single dominant feature of the response is a broad continuum centered at the Γ point, previously identified as a signature of fractionalized excitations. This provides compelling evidence that a field-induced QSL state has been achieved. Copyright © 2017, The Authors. All rights reserved.

关键词： Quantum theory

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Unexpected enhancement of three-dimensional low-energy spin correlations in quasi-two-dimensional fe1+yte1−xsex system at high temperature

arXiv

引用

arXiv 2017年

作者： Xu, Zhijun Schneeloch, J.A. Wen, Jinsheng Winn, B.L. Granroth, G.E. Zhao, Yang Gu, Genda Zaliznyak, Igor Tranquada, J.M. Birgeneau, R.J. Xu, Guangyong Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory UptonNY11973 United States NIST Center for Neutron Research National Institute of Standards and Technology GaithersburgMD20877 United States Department of Materials Science and Engineering University of Maryland College ParkMD20742 United States Physics Department University of California BerkeleyCA94720 United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Physics Stony Brook University Stony BrookNY11794 United States National Laboratory of Solid State Microstructures Department of Physics Nanjing University Nanjing210093 China Quantum Condensed Matter Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak RidgeTN37831 United States

We report inelastic neutron scattering measurements of low energy (~ω . 10 meV) magnetic excitations in the "11" system Fe1+yTe1−xSex. The spin correlations are two-dimensional (2D) in the superconducting samples at low temperature, but appear much more three-dimensional when the temperature rises well above Tc ∼ 15 K, with a clear increase of the (dynamic) spin correlation length perpendicular to the Fe planes. The spontaneous change of dynamic spin correlations from 2D to 3D on warming is unexpected and cannot be naturally explained when only the spin degree of freedom is considered. Our results suggest that the low temperature physics in the "11" system, in particular the evolution of low energy spin excitations towards superconducting pairing, is driven by changes in orbital correlations. Copyright © 2017, The Authors. All rights reserved.

关键词： Degrees of freedom (mechanics)

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Magnetic ground state of the Ising-like antiferromagnet DyScO3

arXiv

引用

arXiv 2017年

作者： Wu, L.S. Nikitin, S.E. Frontzek, M. Kolesnikov, A.I. Ehlers, G. Lumsden, M.D. Shaykhutdinov, K.A. Guo, E.-J. Savici, A.T. Gai, Z. Sefat, A.S. Podlesnyak, A. Quantum Condensed Matter Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Max Planck Institute for Chemical Physics of Solids Nöthnitzer Str. 40 Dresden01187 Germany Institut für Festkörper- und Materialphysik Technische Universität Dresden DresdenD-01069 Germany Chemical and Engineering Materials Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Kirensky Institute of Physics Federal Research Center SB RAS Krasnoyarsk660036 Russia Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Center for Nanophase Materials Sciences Chemical Science Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN37831 United States

We report the low temperature magnetic properties of the DyScO3 perovskite, which were characterized by means of single crystal and powder neutron scattering, and by magnetization measurements. Below TN = 3.15 K, Dy3+ moments form an antiferromagnetic structure with an easy axis of magnetization lying in the ab-plane. The magnetic moments are inclined at an angle of ∼ ±28◦ to the b-axis. We show that the ground state Kramers doublet of Dy3+ is made up of primarily |±15/2i eigenvectors and well separated by crystal field from the first excited state at E1 = 24.9 meV. This leads to an extreme Ising single-ion anisotropy, M⌋/Mk ∼ 0.05. The transverse magnetic fluctuations, which are proportional to M⌋2 /Mk2, are suppressed and only moment fluctuations along the local Ising direction are allowed. We also found that the Dy-Dy dipolar interactions along the crystallographic c-axis are 2-4 times larger than in-plane interactions. Copyright © 2017, The Authors. All rights reserved.

关键词： Ground state

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visualization of Biomolecular Structures: State of the Art 17

Visualization of Biomolecular Structures: State of the Art

引用

17th Eurographics Conference on visualization - State of the Art Reports, EuroVis-STAR 2015

作者： Kozlíková, B. Krone, M. Lindow, N. Falk, M. Baaden, M. Baum, D. Viola, I. Parulek, J. Hege, H.-C. Faculty of Informatics Masaryk University Czech Republic Visualization Research Center University of Stuttgart Germany Department of Visual Data Analysis Zuse Institute Berlin Germany Immersive Visualization Group Linköping University Sweden Laboratoire de Biochimie Théorique UPR 9080 CNRS France Department of Informatics University of Bergen Norway Institute of Computer Graphics and Algorithms Vienna University of Technology Austria

ISBN: (纸本)9783905674996

Structural properties of molecules are of primary concern in many fields. This report provides a comprehensive overview on techniques that have been developed in the fields of molecular graphics and visualization with a focus on applications in structural biology. The field heavily relies on computerized geometric and visual representations of three-dimensional, complex, large, and time-varying molecular structures. The report presents a taxonomy that demonstrates which areas of molecular visualization have already been extensively investigated and where the field is currently heading. It discusses visualizations for molecular structures, strategies for efficient display regarding image quality and frame rate, covers different aspects of level of detail, and reviews visualizations illustrating the dynamic aspects of molecular simulation data. The report concludes with an outlook on promising and important research topics to enable further success in advancing the knowledge about interaction of molecular structures. © The Eurographics Association 2015.

关键词： visualization

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Electron doping evolution of the magnetic excitations in NaFe1−xCoxAs

引用

Physical Review B 2016年第21期93卷 214506-214506页

作者： Scott V. Carr Chenglin Zhang Yu Song Guotai Tan Yu Li D. L. Abernathy M. B. Stone G. E. Granroth T. G. Perring Pengcheng Dai Department of Physics and Astronomy Rice University Houston Texas 77005 USA Department of Physics Beijing Normal University Beijing 100875 China Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA ISIS Facility Rutherford Appleton Laboratory Chilton Didcot Oxfordshire OX11 0QX United Kingdom

We use time-of-flight (TOF) inelastic-neutron-scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1−xCoxAs with x=0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden, and suppress low-energy (E≤80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high-energy (E>80 meV) spin excitations are weakly Co-doping-dependent. Integration of the local spin dynamic susceptibility χ′′(ω) of NaFe1−xCoxAs reveals a total fluctuating moment of 3.6 μB2/Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in Co-overdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel the Ni-doping evolution of spin excitations in BaFe2−xNixAs2 in spite of the differences in crystal structures and Fermi surface evolution in these two families of iron pnictides, thus confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping-dependent high-energy spin excitations result from localized moments.

关键词： Spin fluctuations Spin waves Superconductivity Pnictides Superconductors Unconventional superconductors Inelastic neutron scattering

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Light atom quantum oscillations in UC and US

引用

Physical Review B 2016年第1期93卷 014306-014306页

作者： Yuen Yiu A. A. Aczel G. E. Granroth D. L. Abernathy M. B. Stone W. J. L. Buyers J. Y. Y. Lin G. D. Samolyuk G. M. Stocks S. E. Nagler Department of Physics and Astronomy University of Tennessee Knoxville Tennessee 37996 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Canadian Neutron Beam Centre Canadian Nuclear Laboratories Chalk River Ontario Canada K0J 1J0 California Institute of Technology Pasadena California 91125 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

High-energy vibrational scattering in the binary systems UC and US is measured using time-of-flight inelastic neutron scattering. A clear set of well-defined peaks equally separated in energy is observed in UC, corresponding to harmonic oscillations of the light C atoms in a cage of heavy U atoms. The scattering is much weaker in US and only a few oscillator peaks are visible. We show how the difference between the materials can be understood by considering the neutron scattering lengths and masses of the lighter atoms. Monte Carlo ray tracing is used to simulate the scattering, with near quantitative agreement with the data in UC, and some differences with US. The possibility of observing anharmonicity and anisotropy in the potentials of the light atoms is investigated in UC. Overall, the observed data is well accounted for by considering each light atom as a single atom isotropic quantum harmonic oscillator.

关键词： Phonons Inelastic neutron scattering Monte Carlo methods

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Pressure effect on hydrogen tunneling and vibrational spectrum in α-Mn

引用

Physical Review B 2016年第13期94卷 134301-134301页

作者： A. I. Kolesnikov A. Podlesnyak R. A. Sadykov V. E. Antonov M. A. Kuzovnikov G. Ehlers G. E. Granroth Chemical and Engineering Materials Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Institute for High Pressure Physics RAS 108840 Moscow Troitsk Russia Institute for Nuclear Research RAS 117312 Moscow Russia Institute of Solid State Physics RAS 142432 Chernogolovka Moscow Region Russia Institute of Physical Chemistry PAS 01-224 Warsaw Poland Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

The pressure effect on the tunneling mode and vibrational spectra of hydrogen in α−MnH0.07 has been studied by inelastic neutron scattering. Applying hydrostatic pressure of up to 30 kbar is shown to shift both the hydrogen optical modes and the tunneling peak to higher energies. First-principles calculations show that the potential for hydrogen in α-Mn becomes overall steeper with increasing pressure. At the same time, the barrier height and its extent in the direction of tunneling decrease and the calculations predict significant changes of the dynamics of hydrogen in α-Mn at 100 kbar, when the estimated tunneling splitting of the hydrogen ground state exceeds the barrier height.

关键词： Pressure effects Inelastic neutron scattering

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Thermal evolution of antiferromagnetic correlations and tetrahedral bond angles in superconducting FeTe1−xSex

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Physical Review B 2016年第10期93卷 104517-104517页

作者： Zhijun Xu J. A. Schneeloch Jinsheng Wen E. S. Božin G. E. Granroth B. L. Winn M. Feygenson R. J. Birgeneau Genda Gu I. A. Zaliznyak J. M. Tranquada Guangyong Xu Physics Department University of California Berkeley California 94720 USA Materials Science Division Lawrence Berkeley National Laboratory Berkeley California 94720 USA Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA Department of Physics and Astronomy Stony Brook University Stony Brook New York 11794 USA Center for Superconducting Physics and Materials National Laboratory of Solid State Microstructures and Department of Physics Nanjing University Nanjing 210093 China Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Quantum Condensed Matter Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Chemical and Engineering Materials Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1−xSex. We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Finally, we also present powder neutron diffraction results for lattice parameters in FeTe1−xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3d orbitals.

关键词： PHYSICS periodicals ANTIFERROMAGNETISM IRON compounds BOND angles

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Numerical examination of a model rotor in brownout conditions

Numerical examination of a model rotor in brownout condition...

引用

70th American Helicopter Society International Annual Forum 2014

作者： Kutz, Benjamin M. Günther, Tobias Rumpf, Andreas Kuhn, Alexander University of Stuttgart Institute of Aerodynamics and Gasdynamics Germany University of Magdeburg Visual Computing Group Germany Zuse Institute Berlin Visualization and Data Analysis Germany

ISBN: (纸本)9781632666918

In the present study a flow simulation of a rotor hovering in ground effect was performed and compared to an experimental study from literature. Different reconstruction schemes in the finite volume flow solver were employed, leading to a computation of second and fifth order accuracy in space. The higher order computation was also performed on different grids with six and 23 million grid cells. The integral simulation values were compared to the experimental results and other literature, showing good agreement. Further on, the vortex conservation of the several schemes was compared. The higher order computation yields a much longer vortex preservation and a much better shape approximation, especially with a fine spatial resolution of the computational domain. Moreover, brownout simulations were done in a one-way coupled post processing mode of the flow computation. The results show that a good preservation of the vortices is crucial for a following brownout simulation, which leads to the necessity of a fine resolution and high order computations. The influence of the particle size was examined, leading to the finding that especially a mix of big and small particles in the sediment bed may lead to severe brownout conditions, when flying near the ground. The blade tip vortices are interacting with the sediment and are one of the main drivers of particle entrainment in brownout conditions. ©2014. All rights reserved.

关键词： Vortex flow

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