MaterialVis: Material visualization tool using direct volume and surface rendering techniques

Cataloged from PDF version of article.Visualization of the materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called Material Vis. Unlike the existing tools, Material Vis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. Material Vis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, Material Vis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography. (C) 2014 Elsevier Inc. All rights reserved

Two-dimensional shear modulus of a Langmuir foam

We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by applying a mechanical perturbation, and simultaneously image it by Brewster angle microscopy. We determine the foam stress tensor (through a determination of the 2D gas-liquid line tension, 2.35 $\pm$ 0.4 pJ$\cdot$m$^{-1}$) and the statistical strain tensor, by analyzing the images of the deformed structure. We deduce the 2D shear modulus of the foam, $\mu= 38 \pm 3 \mathrm{nN}\cdot \mathrm{m}^{-1}$. The foam effective rigidity is predicted to be $35 \pm 3 \mathrm {nN}\cdot \mathrm {m}^{- 1}$, which agrees with the value $37.5 \pm 0.8 \mathrm {nN}\cdot \mathrm {m}^{-1}$ obtained in an independent mechanical measurement.Comment: submitted May 12, 2003 ; resubmitted Sept 9, 200

Ordering intermetallic alloys by ion irradiation: a way to tailor magnetic media

Combining He ion irradiation and thermal mobility below 600K, we both trigger and control the transformation from chemical disorder to order in thin films of an intermetallic ferromagnet (FePd). Kinetic Monte Carlo simulations show how the initial directional short range order determines order propagation. Magnetic ordering perpendicular to the film plane was achieved, promoting the initially weak magnetic anisotropy to the highest values known for FePd films. This post-growth treatment should find applications in ultrahigh density magnetic recording.Comment: 7 pages, 3 Figure

Comparison of Different Parallel Implementations of the 2+1-Dimensional KPZ Model and the 3-Dimensional KMC Model

We show that efficient simulations of the Kardar-Parisi-Zhang interface growth in 2 + 1 dimensions and of the 3-dimensional Kinetic Monte Carlo of thermally activated diffusion can be realized both on GPUs and modern CPUs. In this article we present results of different implementations on GPUs using CUDA and OpenCL and also on CPUs using OpenCL and MPI. We investigate the runtime and scaling behavior on different architectures to find optimal solutions for solving current simulation problems in the field of statistical physics and materials science.Comment: 14 pages, 8 figures, to be published in a forthcoming EPJST special issue on "Computer simulations on GPU

The symmetric-Toeplitz linear system problem in parallel

[EN] Many algorithms exist that exploit the special structure of Toeplitz matrices for solving linear systems. Nevertheless, these algorithms are difficult to parallelize due to its lower computational cost and the great dependency of the operations involved that produces a great communication cost. The foundation of the parallel algorithm presented in this paper consists of transforming the Toeplitz matrix into a another structured matrix called Cauchy¿like. The particular properties of Cauchy¿like matrices are exploited in order to obtain two levels of parallelism that makes possible to highly reduce the execution time. The experimental results were obtained in a cluster of PC¿s.Supported by Spanish MCYT and FEDER under Grant TIC 2003-08238-C02-02Alonso-Jordá, P.; Vidal Maciá, AM. (2005). The symmetric-Toeplitz linear system problem in parallel. Computational Science -- ICCS 2005,Pt 1, Proceedings. 3514:220-228. https://doi.org/10.1007/11428831_28S2202283514Sweet, D.R.: The use of linear-time systolic algorithms for the solution of toeplitz problems. k Technical Report JCU-CS-91/1, Department of Computer Science, James Cook University, Tue, 23 April 1996 15, 17, 55 GMT (1991)Evans, D.J., Oka, G.: Parallel solution of symmetric positive definite Toeplitz systems. Parallel Algorithms and Applications 12, 297–303 (1998)Gohberg, I., Koltracht, I., Averbuch, A., Shoham, B.: Timing analysis of a parallel algorithm for Toeplitz matrices on a MIMD parallel machine. Parallel Computing 17, 563–577 (1991)Gallivan, K., Thirumalai, S., Dooren, P.V.: On solving block toeplitz systems using a block schur algorithm. In: Proceedings of the 23rd International Conference on Parallel Processing, Boca Raton, FL, USA, vol. 3, pp. 274–281. CRC Press, Boca Raton (1994)Thirumalai, S.: High performance algorithms to solve Toeplitz and block Toeplitz systems. Ph.d. th., Grad. College of the U. of Illinois at Urbana–Champaign (1996)Alonso, P., Badía, J.M., Vidal, A.M.: Parallel algorithms for the solution of toeplitz systems of linear equations. In: Wyrzykowski, R., Dongarra, J., Paprzycki, M., Waśniewski, J. (eds.) PPAM 2004. LNCS, vol. 3019, pp. 969–976. Springer, Heidelberg (2004)Anderson, E., et al.: LAPACK Users’ Guide. SIAM, Philadelphia (1995)Blackford, L., et al.: ScaLAPACK Users’ Guide. SIAM, Philadelphia (1997)Alonso, P., Badía, J.M., González, A., Vidal, A.M.: Parallel design of multichannel inverse filters for audio reproduction. In: Parallel and Distributed Computing and Systems, IASTED, Marina del Rey, CA, USA, vol. II, pp. 719–724 (2003)Loan, C.V.: Computational Frameworks for the Fast Fourier Transform. SIAM Press, Philadelphia (1992)Heinig, G.: Inversion of generalized Cauchy matrices and other classes of structured matrices. Linear Algebra and Signal Proc., IMA, Math. Appl. 69, 95–114 (1994)Gohberg, I., Kailath, T., Olshevsky, V.: Fast Gaussian elimination with partial pivoting for matrices with displacement structure. Mathematics of Computation 64, 1557–1576 (1995)Alonso, P., Vidal, A.M.: An efficient and stable parallel solution for symmetric toeplitz linear systems. TR DSIC-II/2005, DSIC–Univ. Polit. Valencia (2005)Kailath, T., Sayed, A.H.: Displacement structure: Theory and applications. SIAM Review 37, 297–386 (1995

Inter- and intragrain currents in bulk melt-grown YBaCuO rings

A simple contactless method suitable to discern between the intergrain (circular) current, which flows in the thin superconducting ring, and the intragrain current, which does not cross the weakest link, has been proposed. At first, we show that the intergrain current may directly be estimated from the magnetic flux density $B(\pm z_0)$ measured by the Hall sensor positioned in the special points $\pm z_0$ above/below the ring center. The experimental and the numerical techniques to determine the value $z_0$ are discussed. Being very promising for characterization of a current flowing across the joints in welded YBaCuO rings (its dependencies on the temperature and the external magnetic field as well as the time dissipation), the approach has been applied to study corresponding properties of the intra- and intergrain currents flowing across the $a$-twisted grain boundaries which are frequent in bulk melt-textured YBaCuO samples. We present experimental data related to the flux penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin state and during the field reversal. The shielding properties and their dependence on external magnetic fields are also studied. Besides, we consider the flux creep effects and their influence on the current re-distribution during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version, corrections to perturbing effects near the weak links are introduced, one more figure is added. lin

Strongly linked current flow in polycrystalline forms of the new superconductor MgB2

The discovery of superconductivity at 39 K in MgB2[1] raises many issues. One of the central questions is whether this new superconductor resembles a high-temperature-cuprate superconductor or a low-temperature metallic superconductor in terms of its current carrying characteristics in applied magnetic fields. In spite of the very high transition temperatures of the cuprate superconductors, their performance in magnetic fields has several drawbacks[2]. Their large anisotropy restricts high bulk current densities to much less than the full magnetic field-temperature (H-T) space over which superconductivity is found. Further, weak coupling across grain boundaries makes transport current densities in untextured polycrystalline forms low and strongly magnetic field sensitive[3,4]. These studies of MgB2 address both issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature of our samples, supercurrents flow throughout without the strong sensitivity to weak magnetic fields characteristic of Josephson-coupled grains[3]. Magnetization measurements over nearly all of the superconducting H-T plane show good temperature scaling of the flux pinning force, suggestive of a current density determined by flux pinning. At least two length scales are suggested by the magnetization and magneto optical (MO) analysis but the cause of this seems to be phase inhomogeneity, porosity, and minority insulating phase such as MgO rather than by weakly coupled grain boundaries. Our results suggest that polycrystalline ceramics of this new class of superconductor will not be compromised by the weak link problems of the high temperature superconductors, a conclusion with enormous significance for applications if higher temperature analogs of this compound can be discovered

High magnetic field scales and critical currents in SmFeAs(O,F) crystals: promising for applications

Superconducting technology provides most sensitive field detectors, promising implementations of qubits and high field magnets for medical imaging and for most powerful particle accelerators. Thus, with the discovery of new superconducting materials, such as the iron pnictides, exploring their potential for applications is one of the foremost tasks. Even if the critical temperature Tc is high, intrinsic electronic properties might render applications rather difficult, particularly if extreme electronic anisotropy prevents effective pinning of vortices and thus severely limits the critical current density, a problem well known for cuprates. While many questions concerning microscopic electronic properties of the iron pnictides have been successfully addressed and estimates point to a very high upper critical field, their application potential is less clarified. Thus we focus here on the critical currents, their anisotropy and the onset of electrical dissipation in high magnetic fields up to 65 T. Our detailed study of the transport properties of optimally doped SmFeAs(O,F) single crystals reveals a promising combination of high (>2 x 10^6 A/cm^2) and nearly isotropic critical current densities along all crystal directions. This favorable intragrain current transport in SmFeAs(O,F), which shows the highest Tc of 54 K at ambient pressure, is a crucial requirement for possible applications. Essential in these experiments are 4-probe measurements on Focused Ion Beam (FIB) cut single crystals with sub-\mu\m^2 cross-section, with current along and perpendicular to the crystallographic c-axis and very good signal-to-noise ratio (SNR) in pulsed magnetic fields. The pinning forces have been characterized by scaling the magnetically measured "peak effect"