Resources

Bruce M. Boghosian, Center for Computational Science, Boston University
Peter V. Coveney, Department of Chemistry, Queen Mary and Westfield College, University of London

Lattice models have been used to study the equilibrium properties of amphiphilic fluids for over a decade now. many interesting questions about these fluids, however, center on their behavior away from equilibrium. Droplet growth rates, fluctuations of interfaces loaded with surfactang, vesicle formation, and rheology in the presence of shearing flow, for example, all involve hydrodynamics, and therefore require a model with a conserved momentum. In our research, we present recent simulational results from a three-dimensional lattice-gass hydrodynamic model of amphiphilic fluids. These results include spherical and "wormlike" micelle formation, sponge sphases and lamellae.

Norman J. Zabusky and Deborah Silver, Laboratory for Visiometrics and Modeling, Mechanical & Aerospace Engineering & CAIP Center, Rutgers, The State University of New Jersey

The goal of large-scale simulations and experiments in computational science and technology is a quantitative and mathematical understanding for the model being investigated. We are employing the visiometrics and modeling paradigm. Visiometrics involves two categories of related processes:

• Visualization (including data projection, image rendering, feature extraction and classification), and
• Quantification (or feature measurement, space-time feature identification, and feature tracking).

Visualization involves projecting the data into alternate spaces (e.g. wave number space for spectra) or lower dimensional spaces (e.g. space-time diagrams), rendering the features, and isolating observed coherent" regions. Examples of coherent structures from fluid dynamics include: wave packets; shock waves; solitons; eddies; holes; bubbles; rings; tubes; spikes; etc.

Quantification involves measuring properties of coherent features (or objects) that are defined according to a physically based rule or that lie above some threshold. This includes: content (volume, mass, charge. circulation, etc. ); moments about extrema (e.g. quadratic forms of thresholded objects); gradients, curvatures, torsion's of skeletons of tubular or layered domains; critical points of velocity fields; eigenvalues and eigenvectors of tensor fields, etc.; and properties of space-time trajectories of these objects in the original or lower-dimensional (projected) spaces.

We are developing tools to easily access, manipulate, extract, track and archive essential features of one or more computer simulations, or laboratory or field experiments. The cogent assimilation and juxtaposition of measured and simulated data sets and their thresholded projections into lower dimensions will provide insights into the causes of observed phenomena. These insights will show the way toward formulating hierarchies of mathematical models and will result in increased reliability of predictions.

Areas of interest include novel algorithms to manage, visualize and quantify massive data sets using numerical, geometrical and graphical techniques. Quantification encompasses identifying coherent regions and structures, extracting these regions, simplifying them and fitting terse mathematical descriptions to them. Parallel algorithms for visualizing, quantifying, and managing hierarchical datasets are being developed.

Direct numerical simulations in computational fluid dynamics provide the data sets for these studies, including simulations done on a CRAY Y/MP and C-90 at PSC and the Connection Machine CM5 at NCSA. We are presently studying: 2D and 3D shock-interface and shock-bubble interactions and compressible coherent structures and turbulence; and 2D vortex dynamics and turbulence via pseudospectral and contour dynamics/surgery codes; 3D vortex tube interactions, reconnection, intermittency and turbulence via pseudospectral and Biot-Savart codes.

Tom Mehlhorn, Sandia National Laboratories*, Albuquerque, NM

Three dimensional radiation magneto-hydrodynamic (rad-MHD) simulations are required to understand the radiation production scaling of wire array z-pinches imploded by pulsed power drivers. Sandia is developing a rad-MHD version of ALEGRA, an arbitrary Lagrangian-Eulerian material dynamics code, to perform such simulations on various platforms, including the ASCI Red Machine. Experimentally, Sandia has generated z-pinch powers up to 280 TW utilizing tungsten wire arrays on the Z Machine. Increasing the number of wires in the array appears to decrease the perturbation seed to the magnetic Rayleigh-Taylor (MRT) instability and decrease the FWHM of the radiation pulse. The scaling of radiation pulse width with initial perturbation amplitude has been studied primarily with 2-D simulations. We report on the first massively parallel simulations of the evolution of the MRT instability in three dimensions.

* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Jon J.V. Maestri, Rubin H. Landau, Physics Department, Oregon State University
Manuel J. Paez, Physics Department, University of Antioquia, Medellin, Colombia

A simple and explicit technique for the numerical solution of the two-particle, time-dependent Schrvdinger equation is assembled and tested. The technique can handle interparticle potentials that are arbitrary functions of the coordinates of each particle, arbitrary initial and boundary conditions, and multi-dimensional equations. Plots and animations are given here and on the World Wide Web of the scattering of two wavepackets in one dimension.

Brian Schlatter, Rubin H. Landau, Department of Physics
Keith Vertanen, Department of Computer Science
Oregon State University, Corvallis, OR 97331

We have implemented a fluid flow simulation using the smoothed particle hydrodynamics method. The implementation runs in parallel on distributed memory machines using the MPI message passing libraries. Shown in the image is a color contour plot of the velocity field for flow in a channel around an object (the Beaver).

M. Ishida and Y. Zempo, (Sumitomo Chemical Co. Ltd.)
S. Ohnishi (NEC Corp.)
A. Fukumoto, K. Miwa (TOYOTA Central R&D Labs.)
S. Itoh (TOSHIBA Corp.)
H. Odaka (Asahi Glass Co. Ltd.)
M. Iwasawa, T. Saito (Sony Corp.)
A. Kato, H. Rikukawa (FDK Corp.)
M. Nishitsuka (PIONEER Electronic Corp.)
M. Takimoto, H. Shibuki, Y. Ohtani (Fuji Research Institute Corp.)
Y. Inoue, M. Tanoura (Mitsubishi Heavy Industries, Ltd.)

As a research community for computational materials science and related fields, the CAMP project was established in 1990 by researchers and engineers in Japanese industries to share knowledge and techniques of computational methods, and to make a base code for anyone to handle easily. Our first code named CAMP-Atami, a Car-Parrinello type of program, was available for public use in 1994. Several new programs are being developed; one in a plane wave basis, one in a mixed basis, one by an adaptive coordinate method, one based on parallel computing, one for pseudopotential generation, etc. Recently published computational techniques are also involved in the programs.

J. Bernholc, E. L. Briggs, M. Buongiorno Nardelli, K. Rapcewicz, C. Roland and M. Wensell, North Carolina State University

Large-scale ab initio dynamics can reliably predict the atomic pathways of phase transformations, failure mechanisms under mechanical load and even chemical reactions. We use interactive 3D visualizations, videos and images to illustrate the impact of modern visualization techniques on both the initial analysis and presentations towide audiences. The specific examples include C60 dynamics, surface melting of Si, ductile and brittle behavior of carbon nanotubes, and surfaces of nitride semiconductors.

V.V. Godlevsky, M. Jain, J.J. Derby and J.R. Chelikowsky, Department of Chemical Engineering and Materials Science, Minnesota Supercomputing Institute, University of Minnesota

One of the most exciting developments in computational material science has been the development of simulation methods using quantum forces. It is no longer necessary to employ empirical interatomic potentials in molecular dynamics simulations. We illustrate these techniques by examining liquid ZnTe. This is part of a larger project encompassing II-VI liquid semiconductors, e.g., to date we have examined ZnTe, CdTe and HgTe in the liquid and solid state. One of the most interesting issues in these materials concerns the conductivity of the liquid state. Most Group IV and III-VI semiconductors are metallic in the liquid state; however, some II-VI semiconductors remain semiconducting in the melt. In order to examine this problem in more detail, we have calculated the conductivity of a prototypical III-V semiconductor (GaAs) and compared its properties to II-VI semiconductors. Our simulations use the pseudopotential density functional method (PDFM) to calculate quantum forces in the melt. We prepare a liquid state ensemble using supercells and Langevin dynamics to thermalize the liquid. Our demonstration illustrates the microstructure of the liquid state and the self-diffusion of Zn and Te within the melt. We summarize our studies of II-VI semiconductors and illustrate how the microstructure of the liquid can affect the conductivity of the liquid state. We will also discuss why it may be difficult to grow Te II-VI's from the melt.

Reference: V. Godlevsky M. Jain, J.J. Derby and J.R. Chelikowsky, Phys. Rev. Lett. 81, 4959 (1998)

Mark Miller, Wai-Mo Suen and Malcolm Tobias, NCSA/Potsdam/Washington U Collaboration

General Relativistic Astrophysics---astrophysics that involves strong and dynamical gravitational fields requiring the full Einstein equations for its understanding---is becoming a promising research area, due to the large amount of data in high energy astronomy, and to the great promise of gravitational wave astronomy made possible by the Laser Interferometer Gravitational Wave Observatories, LIGO/VIRGO and LISA. In particular, Computational General Relativistic Astrophysics, with the recent stunning increases in computer power, may hold the key to the understanding of many observations in high energy astronomy and gravitational wave astronomy.

We show a simulation of two neutron stars in a grazing collision based on the full Einstein equations coupled to general relativistic hydrodynamic equations. The coalescences of neutron star binaries have attracted much attention as sources of gravitational radiation and candidates of gamma-ray burst.

The simulation is carried out with a 3D code called "Cactus" that is currently being developed by our NCSA/Potsdam/Wash U Numerical Relativity Collaboration, together with other research groups in the community. The study of neutron star coalescences is performed as part of the NASA Neutron Star Grand Challenge Project (NASA HPCC NCCS5-153). The computation is carried out at the NSF SuperComputing Centers under National Resource Allocation MCA 93S025.

Mark Miller, Wai-Mo Suen and Malcolm Tobias, NCSA/Potsdam/Washington U Collaboration

General Relativistic Astrophysics---astrophysics that involves strong and dynamical gravitational fields requiring the full Einstein equations for its understanding---is becoming a promising research area, due to the large amount of data in high energy astronomy, and to the great promise of gravitational wave astronomy made possible by the Laser Interferometer Gravitational Wave Observatories, LIGO/VIRGO and LISA. In particular, Computational General Relativistic Astrophysics, with the recent stunning increases in computer power, may hold the key to the understanding of many observations in high energy astronomy and gravitational wave astronomy.

We show a simulation of two neutron stars in a grazing collision based on the full Einstein equations coupled to general relativistic hydrodynamic equations. The coalescences of neutron star binaries have attracted much attention as sources of gravitational radiation and candidates of gamma-ray burst.

The simulation is carried out with a 3D code called "Cactus" that is currently being developed by our NCSA/Potsdam/Wash U Numerical Relativity Collaboration, together with other research groups in the community. The study of neutron star coalescences is performed as part of the NASA Neutron Star Grand Challenge Project (NASA HPCC NCCS5-153). The computation is carried out at the NSF SuperComputing Centers under National Resource Allocation MCA 93S025.

Keith M. Glassford, Molecular Simulations Inc.

The advances in theoretical and computational methods combined with the rapid progress in computer hardware has now made it possible to investigate the material properties from the sub-atomic scale, through the atomic and molecular scale, up to the mesoscale level. MSI will discuss how computer modeling can help scientists and engineers predict material properties, design and characterize new materials, and optimize existing processes using molecular modeling software. The focus will be towards the chemical and materials industry using MSI's software to understand the chemistry and physics of molecules, polymers and bulk materials using various simulation strategies ranging from force fields to first principles quantum mechanics.