Plasma estimation: A noise cancelling application

In this paper we discuss the application of a noise cancelling technique to extract energy storage information from sensors occurring during fusion reactor experiments on the Tandem Mirror Experiment-Upgrade (TMX-U) at the Lawrence Livermore National Laboratory (LLNL). We show how this technique can be used to decrease the uncertainty in the corresponding sensor measurements used for diagnostics in both real-time and post-experimental environments. We analyze the performance of the algorithm on the sensor data and discuss the various tradeoffs. The algorithm suggested is designed using SIG. an interactive signal processing package developed at LLNL.     

The NMFECC cray time-sharing system

The National Magnetic Fusion Energy Computer Center (NMFECC) at the Lawrence Livermore National Laboratory (LLNL) has implemented a simple, yet powerful interactive operating system, the Cray Time-Sharing System (CTSS), on a Cray-1 supercomputer. CTSS augments the multi-programming batch facilities normally found in supercomputer systems with many of the interactive services typical of interactive minicomputer systems. This paper gives some of the historical background leading to CTSS and gives an overview of the system that emphasizes the strong points or unusual features such as multiple channels, decentralized control of resources, priorities and program scheduling, system recovery, and on-line documentation.     

High-resolution multiprojector display walls

Meeting the demands of the current tera-scale visualization community requires the use of large- and small-scale tiled displays. The Lawrence Livermore National Laboratory (LLNL) efforts in this area have led to the creation of one of the largest interactive tiled displays built to date, and a number of new efforts for “personal” tiled displays. Visualization hardware and software now being built will display up to 15 times the number of pixels in a typical desktop display. We outline the system implemented at LLNL for the creation and support of large, tiled, multi-pipe graphics displays. The system builds on a simple, portable, parallel API for tiling OpenGL commands in parallel to multiple contexts on a set of X servers. This API has allowed us to retrofit existing visualization and analysis codes to support these displays with very little effort. While this work represents a first step toward the ultimate goal of scalable visualization in individual office spaces, the result has been the creation of useful new visualization workspaces and tools for our users     

Electromagnetic signal processing An estimation/identification application

The response of an object subjected to high energy, transient electromagnetic fields sometimes called an electromagnetic pulse (EMP) is an important issue in the survivability of electronic systems (e.g. aircraft, computer systems, etc.), especially when the field has been generated by a high-altitude nuclear burst. The characterization of transient response information is a matter of national concern. In this paper, estimation and identification techniques are applied to: (1) improve signal processing at a test facility, and (2) parameterize a particular object response.First, the application of identification-based signal processing techniques to improve signal levels at the Lawrence Livermore National Laboratory (LLNL) Electromagnetic Test Facility is discussed. Models of test equipment are identified and then utilized in processing schemes to enhance or recover the desired signals. Parametric models of objects under test are identified from the enhanced data in order to extrapolate responses to threat levels.     

A survey of high level frameworks in block-structured adaptive mesh refinement packages

Over the last decade block-structured adaptive mesh refinement (SAMR) has found increasing use in large, publicly available codes and frameworks. SAMR frameworks have evolved along different paths. Some have stayed focused on specific domain areas, others have pursued a more general functionality, providing the building blocks for a larger variety of applications. In this survey paper we examine a representative set of SAMR packages and SAMR-based codes that have been in existence for half a decade or more, have a reasonably sized and active user base outside of their home institutions, and are publicly available. The set consists of a mix of SAMR packages and application codes that cover a broad range of scientific domains. We look at their high-level frameworks, their design trade-offs and their approach to dealing with the advent of radical changes in hardware architecture. The codes included in this survey are BoxLib, Cactus, Chombo, Enzo, FLASH, and Uintah.     

The Origins of the Teapot

Are you interested in more articles of this type? Are you interested in data (such as the teapot data) or code or both? Do you have public domain data and/or code that you would be willing to share? Please send your answers and comments to chip Hatfield, Lawrence Livermore National Laboratory, PO Box 5504, L-156, Livermore, CA 94550 or HATFIELD@LLL-ICDC.ARPA.     

Three-Dimensional Numerical Model of the Interaction of Laser Radiation with the Plasma of a Plastic Target

The effect of generation of high-energy protons and carbon nuclei is identified in the threedimensional model of the interaction of a high-power electromagnetic field with plasma with supercritical density by the numerical solution of the Vlasov–Maxwell equations. The effect was first discovered in 2000 in experiments carried out at the Lawrence Livermore National Laboratory (United States) using the petawatt laser.     

The Electronics Engineer's Design Station

A prototype graphics system at Lawrence Livermore National Laboratory takes advantage of menu-driven, interactive techniques to simplify the tasks of electronics designers.     

The butterfly barrier

We describe and algorithm for barrier synchronization that requires only read and write to shared store. The algorithm is faster than the traditionallocked counter approach for two processors and has an attractive log₂ N time scaling for largerN. The algorithm is free of hot spots and critical regions and requires a shared memory bandwidth which grows linearly withN, the number of participating processors. We verify the technique using both a real shared memory multiprocessor, for numbers of processors up to 30, and a shared memory multiprocessor simulator, for number of processors up to 256.Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.     

A novel dynamic load balancing scheme for parallel systems

Adaptive mesh refinement (AMR) is a type of multiscale algorithm that achieves high resolution in localized regions of dynamic, multidimensional numerical simulations. One of the key issues related to AMR is dynamic load balancing (DLB), which allows large-scale adaptive applications to run efficiently on parallel systems. In this paper, we present an efficient DLB scheme for structured AMR (SAMR) applications. This scheme interleaves a grid-splitting technique with direct grid movements (e.g., direct movement from an overloaded processor to an underloaded processor), for which the objective is to efficiently redistribute workload among all the processors so as to reduce the parallel execution time. The potential benefits of our DLB scheme are examined by incorporating our techniques into a SAMR cosmology application, the ENZO code. Experiments show that by using our scheme, the parallel execution time can be reduced by up to 57% and the quality of load balancing can be improved by a factor of six, as compared to the original DLB scheme used in ENZO.     

A program to determine the radiation spectra due to a single atomic-subshell ionisation by a particle or due to deexcitation or decay of radionuclides

The computer program IMRDEC has been developed to determine the radiation spectra due to a single atomic-subshell ionisation of a stable atom by a particle, or due to the atomic deexcitation or decay of nuclides. The data needed to describe the deexcitation or decay scheme of the mother atoms are obtained from the Evaluated Nuclear Structure Data File (ENSDF) maintained at Brookhaven National Laboratory; this results in the simplest possible input specification. The atomic data as well as the atomic relaxation probabilities are taken from the Evaluated Atomic Data Library (EADL) from Lawrence Livermore National Laboratory. The program IMRDEC calculates the radiation spectra (inclusive the atomic relaxation cascades) optionally, using the deterministic or the Monte Carlo method. The deterministic method results in a much shorter calculation time per nuclide. Due to the many assumptions that worldwide still have to be made in determining the atomic relaxation probabilities as well as in calculating the atomic relaxation, the deterministic method seems to be a small source of inaccuracy.     

An Algorithm for Projecting Points onto a Patched CAD Model

We are interested in building structured overlap-ping grids for geometries defined by Computer-Aided-Design (CAD) packages. Geometric information defining the boundary surfaces of a computation domain is often provided in the form of a collection of possibly hundreds of trimmed patches. The first step in building an overlapping volume grid on such a geometry is to build overlapping surface grids. A surface grid is typically built using hyperbolic grid generation; starting from a curve on the surface, a grid is grown by marching over the surface. A given hyperbolic grid will typically cover many of the underlying CAD surface patches. The fundamental operation needed for building surface grids is that of projecting a point in space onto the closest point on the CAD surface. We describe a fast and robust algorithm for performing this projection which makes use of a fairly coarse global triangulation of the CAD geometry. Before the global triangulation is constructed the connectivity of the model is determined by an edge-matching algorithm which corrects for gaps and overlaps between neighbouring patches. ID="A1" Correspondence and offprint requests to: Dr. W. D. Henshaw, Center for Applied Scientific Computing, L-661, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA. E-mail: henshaw@llnl.gov     

Newton-Krylov-FAC methods for problems discretized on locally refined grids

Many problems in computational science and engineering are nonlinear and time-dependent. The solutions to these problems may include spatially localized features, such as boundary layers or sharp fronts, that require very fine grids to resolve. In many cases, it is impractical or prohibitively expensive to resolve these features with a globally fine grid, especially in three dimensions. Adaptive mesh refinement (AMR) is a dynamic gridding approach that employs a fine grid only where necessary to resolve such features. Numerous AMR codes exist for solving hyperbolic problems with explicit time stepping and some classes of linear elliptic problems. Researchers have paid much less attention to the development of AMR algorithms for the implicit solution of systems of nonlinear equations. Recent efforts encompassing a variety of applications demonstrate that Newton-Krylov methods are effective when combined with multigrid preconditioners. This suggests that hierarchical methods, such as the Fast Adaptive Composite grid (FAC) method of McCormick and Thomas, can provide effective preconditioning for problems discretized on locally refined grids. In this paper, we address algorithm and implementation issues for the use of Newton-Krylov-FAC methods on structured AMR grids. In our software infrastructure, we combine nonlinear solvers from KINSOL and PETSc with the SAMRAI AMR library, and include capabilities for implicit time stepping. We have obtained convergence rates independent of the number of grid refinement levels for simple, nonlinear, Poisson-like, problems. Additional efforts to employ this infrastructure in new applications are underway. Communicated by: G. Wittum     

Real-Time Microcomputer Applications Using LLL Basic

One of the most controversial subjects today is the cost-effectiveness and usefulness of high-level languages in microcomputer applications. Lawrence Livermore Laboratory has been involved with microprocessors since 1972^1,2and as such has constantly been involved with the evaluation of HLL's. The problem becomes even more complicated when the area of real time data acquisition and control is specifically addressed.     

A Standard Best Practice Approach to Acquisition of Secure ICT Products

Abstract

Analysis of Operating System Security, by Janet S. Chin. Lawrence Livermore Laboratory (order from National Technical Information Service, U. S. Department of Commerce, Springfield, VA, 22151). December 2, 1975; 24 pages; $4.50.

Computer Abuse Perpetrators and Vulnerabi- Lities of Computer Systems, by Donn B. Parker. Stanford Research Institute (Report Production, Building 300 B5, 330 Ravenswood Ave., Menlo Park, CAI 94025). December 1975; 27 pages; $5.00.     

Investigating Autonomic Runtime Management Strategies for SAMR Applications

Dynamic structured adaptive mesh refinement (SAMR) techniques along with the emergence of the computational Grid offer the potential for realistic scientific and engineering simulations of complex physical phenomena. However, the inherent dynamic nature of SAMR applications coupled with the heterogeneity and dynamism of the underlying Grid environment present significant research challenges. This paper presents application/system sensitive reactive and proactive partitioning strategies that form a part of the GridARM autonomic runtime management framework. An evaluation using different SAMR kernels and system workloads is presented to demonstrate the improvement in overall application performance.     

KRS: A fast special-purpose database system

The K-Division Retrieval System (KRS) is a group of programs and files maintained by the Lawrence Livermore Laboratory to store and recall data about the geology and events at the Nevada Test Site. KRS consists of two large data files that are updated regularly with new information. This report describes these data files and the interaction necessary to use the specialized programs, obtain access to the information, and arrange the data reports. These programs are run on CDC-7600 computers and are available in public files.     

Towards autonomic application-sensitive partitioning for SAMR applications

Distributed structured adaptive mesh refinement (SAMR) techniques offer the potential for accurate and cost-effective solutions of physically realistic models of complex physical phenomena. However, the heterogeneous and dynamic nature of SAMR applications results in significant runtime management challenges. This paper investigates autonomic application-sensitive SAMR runtime management strategies and presents the design, implementation, and evaluation of ARMaDA, a self-adapting and optimizing partitioning framework for SAMR applications. ARMaDA monitors and characterizes application runtime state, and dynamically selects and invokes appropriate partitioning mechanisms that match current SAMR state and optimize its computational and communication performance. The advantages of the autonomic partitioning capabilities provided by ARMaDA are experimentally demonstrated.     

Texture-based volume rendering of adaptive mesh refinement data

Many phenomena in nature and engineering happen simultaneously on rather diverse spatial and temporal scales. In other words, they exhibit a multi-scale character. A special numerical multilevel technique associated with a particular hierarchical data structure is adaptive mesh refinement (AMR). This scheme achieves locally very high spatial and temporal resolutions. Due to its popularity, many scientists are in need of interactive visualization tools for AMR data. In this article, we present a 3D texture-based volume-rendering algorithm for AMR data that directly utilizes the hierarchical structure. Thereby fast rendering performance is achieved even for high-resolution data sets. To avoid multiple rendering of regions that are covered by grids of different levels of resolution, we propose a space partitioning scheme to decompose the volume into axis-aligned regions of equal-sized cells. Furthermore the problems of interpolation artifacts, opacity corrections, and texture memory limitations are addressed. Published online: November 6, 2002 Correspondence to: R. K?hler