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At least 1,063 records · Page 59

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Supplemental Microalgal DHA and Astaxanthin Affect Astaxanthin Metabolism and Redox Status of Juvenile Rainbow Trout

Microalgal docosahexaenoic acid (DHA) and astaxanthin (AST) may substitute for fish oil and synthetic AST in aquafeeds. This study explored the effects and mechanisms of those substitutions on AST metabolism and redox status of rainbow trout fed plant protein meal (PM)- or fishmeal (FM)-based diets. Two parallel experiments (PM vs. FM) were performed with 612 juvenile rainbow trout for 16 weeks as a 2 × 3 factorial arrangement of treatments with two AST sources (synthetic (SA) vs. microalgal (AA), at 80 mg/kg) and three levels (0, 50, and 100%) of fish oil substitutions with DHA-rich microalgae. The fish oil substitutions exhibit main effects (p < 0.05) and/or interactive effects (p < 0.05) with the source of AST on AST deposition, malondialdehyde and glutathione concentrations, and mRNA levels and activities of major redox enzymes (glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), and superoxide dismutase (SOD)) in the muscle and liver of trout fed both diet series. The AST source produced only differences in tissue AST deposition (p < 0.05) and number of metabolites. In conclusion, the substitutions of fish oil by the DHA-rich microalgae exerted more impacts than those of SA by AA on redox status and functional expression of antioxidant enzymes in the tissues of rainbow trout.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

Dynamics of Laterally Propagating Flames in X-Ray Bursts. I. Burning Front Structure

We investigate the structure of laterally propagating flames through the highly stratified burning layer in an X-ray burst. Two-dimensional hydrodynamics simulations of flame propagation are performed through a rotating plane-parallel atmosphere, exploring the structure of the flame. We discuss the approximations needed to capture the length and timescales at play in an X-ray burst and describe the flame acceleration observed. Finally, our studies complement other multidimensional studies of burning in X-ray bursts.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Cholesky-based experimental design for Gaussian process and kernel-based emulation and calibration.

Gaussian processes and other kernel-based methods are used extensively to construct approximations of multivariate data sets. The accuracy of these approximations is dependent on the data used. This paper presents a computationally efficient algorithm to greedily select training samples that minimize the weighted L p error of kernel-based approximations for a given number of data. The method successively generates nested samples, with the goal of minimizing the error in high probability regions of densities specified by users. The algorithm presented is extremely simple and can be implemented using existing pivoted Cholesky factorization methods. Training samples are generated in batches which allows training data to be evaluated (labeled) in parallel. For smooth kernels, the algorithm performs comparably with the greedy integrated variance design but has significantly lower complexity. Numerical experiments demonstrate the efficacy of the approach for bounded, unbounded, multi-modal and non-tensor product densities. We also show how to use the proposed algorithm to efficiently generate surrogates for inferring unknown model parameters from data using Bayesian inference.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2023

BOXKIT

SF-23-067 BoxKit is a library that provides building blocks to parallelize and scale data science, high performance computing, and machine learning applications for block-structured datasets. Spatial data from simulations and experiments can be accessed and managed using tools available in this library when working with more data analysis oriented packages like SciKit (https://github.com/scikit-learn/scikit-learn) and FlowNet (https://github.com/NVIDIA/flownet2-pytorch)

DHRUV, AKASH↗

NASA NTRS1974

Prediction of compressor stall for distorted and undistorted flow by use of a multistage compressor simulation on the digital computer

Daniele, C. J.↗

NASA NTRS1975

Prediction of compressor stall for distorted and undistorted flow by use of a multistage compressor simulation on the digital computer

A simulation technique is presented for the prediction of compressor stall for axial-flow compressors for clean and distorted inlet flow. The simulation is implemented on the digital computer and uses stage stacking and lumped-volume gas dynamics. The resulting nonlinear differential equations are linearized about a steady-state operating point, and a Routh-Hurwitz stability test is performed on the linear system matrix. Parallel compressor theory is utilized to extend the technique to the distorted inlet flow problem. The method is applied to the eight-stage J85-13 compressor. Analytical stall prediction for the undistorted stall line shows good agreement with experimental results. The predicted stall line for distorted inlet flow is in agreement with experimental results only for large distortion extents and/or low distortion levels. Results for low distortion extents and high distortion level do not agree with experimental results.

Daniele, C. J.↗

NASA NTRS1979

Calculation of transonic aileron buzz

An implicit finite-difference computer code that uses a two-layer algebraic eddy viscosity model and exact geometric specification of the airfoil has been used to simulate transonic aileron buzz. The calculated results, which were performed on both the Illiac IV parallel computer processor and the Control Data 7600 computer, are in essential agreement with the original expository wind-tunnel data taken in the Ames 16-Foot Wind Tunnel just after World War II. These results and a description of the pertinent numerical techniques are included.

Steger, J. L.↗

NASA NTRS1980

An approach to simulation of the finite element machine

The paper describes the simulation approach for the finite element machine (FEM), a special-purpose computer for structural analysis calculations under development at the NASA-Langley Research Center. The FEM consists of an array (1000 or more) of general-purpose microcomputers performing structural analysis in an asychronous parallel manner. A simulator of sufficient flexibility to model the behavior of the FEM on many levels has been designed and coded, and verification has begun using the experimental FEM hardware. The structure of the simulator is described, and preliminary simulation results are presented.

Sawyer, P. L.↗

NASA NTRS1987

Calculations of inlet distortion induced compressor flowfield instability

Calculations are presented predicting the onset of flow instability for a multistage low speed axial compressor operating in circumferentially distorted inlet flow. The most important feature of the model used is that it attempts to properly account for the fluid dynamic interaction between the spoiled and unspoiled sectors of the compressor. The calculations show that there is an approximate stability criterion, the annulus averaged slope of the compressor pressure rise characteristic equal to zero, that is valid whenever the dynamics of the compressor distorted flowfield can be considered independent of the compressor environment. This approximate criterion is used to investigate the relationship between the present model and the parallel compressor model. Further calculations are performed to investigate cases of interest when the dynamics of the flowfield are coupled to the environment. Resonant cases and cases when the distortion is unsteady are studied. In particular, it is shown that rotating distortions which propagate in the rotor direction can have a greater effect on stability margin than stationary or counter-rotational ones. Finally, it is shown that the general predictions of the model are insensitive to the details of the unsteady bladerow dynamics.

Hynes, T. P.↗

NASA NTRS1987

Plasma simulation using the massively parallel processor

Two dimensional electrostatic simulation codes using the particle-in-cell model are developed on the Massively Parallel Processor (MPP). The conventional plasma simulation procedure that computes electric fields at particle positions by means of a gridded system is found inefficient on the MPP. The MPP simulation code is thus based on the gridless system in which particles are assigned to processing elements and electric fields are computed directly via Discrete Fourier Transform. Currently, the gridless model on the MPP in two dimensions is about nine times slower that the gridded system on the CRAY X-MP without considering I/O time. However, the gridless system on the MPP can be improved by incorporating a faster I/O between the staging memory and Array Unit and a more efficient procedure for taking floating point sums over processing elements. The initial results suggest that the parallel processors have the potential for performing large scale plasma simulations.

Lin, C. S.↗

NASA NTRS1989

The isothermal fatigue behavior of a unidirectional SiC/Ti composite and the Ti alloy matrix

The high temperature fatigue behavior of a metal matrix composite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 vol percent of continuous unidirectional SiC fibers was experimentally and analytically evaluated. Isothermal MMC fatigue tests with constant amplitude loading parallel to the fiber direction were performed at 300 and 550 C. Comparative fatigue tests of the Ti-15-3 matrix alloy were also conducted. Composite fatigue behavior and the in-situ stress state of the fiber and matrix were analyzed with a micromechanical model, the Concentric Cylinder Model (CCM). The cyclic stress-strain response of the composite was stable at 300 C. However, an increase in cyclic mean strain foreshortened MMC fatigue life at high strain ranges at 550 C. Fatigue tests of the matrix alloy and CCM analyses indicated this response was associated with stress relaxation of the matrix in the composite.

Gayda, John, Jr.↗

NASA NTRS1988

Benchmarking and performance analysis of the CM-2

A suite of benchmarking routines testing communication, basic arithmetic operations, and selected kernel algorithms written in LISP and PARIS was developed for the CM-2. Experiment runs are automated via a software framework that sequences individual tests, allowing for unattended overnight operation. Multiple measurements are made and treated statistically to generate well-characterized results from the noisy values given by cm:time. The results obtained provide a comparison with similar, but less extensive, testing done on a CM-1. Tests were chosen to aid the algorithmist in constructing fast, efficient, and correct code on the CM-2, as well as gain insight into what performance criteria are needed when evaluating parallel processing machines.

Myers, David W.↗

NASA NTRS1989

CFD in design - A government perspective

Some of the research programs involving the use of CFD in the aerodynamic design process at government laboratories around the United States are presented. Technology transfer issues and future directions in the discipline or CFD are addressed. The major challengers in the aerosciences as well as other disciplines that will require high-performance computing resources such as massively parallel computers are examined.

Kutler, Paul↗

NASA NTRS1988

Quench gases for xenon- (and krypton-) filled proportional counters

Xenon-filled proportional counters are used extensively in astronomy, particularly in the hard X-ray region. The choice of quench gas can have a significant effect on the operating characteristics of the instrument although the data necessary to make the choice are not easily obtainable. Results which detail the performance obtained from both cylindrical and parallel field geometries for a wide variety of readily available, ultrahigh or research grade purity, quench gases are presented.

Ramsey, B. D.↗

NASA NTRS1991

Parallel algorithms for placement and routing in VLSI design

The computational requirements for high quality synthesis, analysis, and verification of very large scale integration (VLSI) designs have rapidly increased with the fast growing complexity of these designs. Research in the past has focused on the development of heuristic algorithms, special purpose hardware accelerators, or parallel algorithms for the numerous design tasks to decrease the time required for solution. Two new parallel algorithms are proposed for two VLSI synthesis tasks, standard cell placement and global routing. The first algorithm, a parallel algorithm for global routing, uses hierarchical techniques to decompose the routing problem into independent routing subproblems that are solved in parallel. Results are then presented which compare the routing quality to the results of other published global routers and which evaluate the speedups attained. The second algorithm, a parallel algorithm for cell placement and global routing, hierarchically integrates a quadrisection placement algorithm, a bisection placement algorithm, and the previous global routing algorithm. Unique partitioning techniques are used to decompose the various stages of the algorithm into independent tasks which can be evaluated in parallel. Finally, results are presented which evaluate the various algorithm alternatives and compare the algorithm performance to other placement programs. Measurements are presented on the parallel speedups available.

Brouwer, Randall Jay↗

NASA NTRS1990

Learning control system design based on 2-D theory - An application to parallel link manipulator

An approach to iterative learning control system design based on two-dimensional system theory is presented. A two-dimensional model for the iterative learning control system which reveals the connections between learning control systems and two-dimensional system theory is established. A learning control algorithm is proposed, and the convergence of learning using this algorithm is guaranteed by two-dimensional stability. The learning algorithm is applied successfully to the trajectory tracking control problem for a parallel link robot manipulator. The excellent performance of this learning algorithm is demonstrated by the computer simulation results.

Geng, Z.↗

NASA NTRS1990

The isothermal fatigue behavior of a unidirectional SiC/Ti composite and the Ti alloy matrix

The high temperature fatigue behavior of a metal matrix composite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn(Ti-15-3) matrix reinforced by 33 volume percent of continuous unidirectional SiC fibers was experimentally and analytically evaluated. Isothermal MMC fatigue tests with constant amplitude loading parallel to the fiber direction were performed at 300 and 550 C. Comparative fatigue tests of the Ti-15-3 matrix alloy were also performed. Composite fatigue behavior and the in situ stress state of the fiber and matrix were analyzed with a micromechanical model, the Concentric Cylinder Model (CCM). The cyclic stress-strain response of the composite was stable at 300 C. However, an increase in cyclic mean strain foreshortened MMC fatigue life at high strain ranges at 550 C. Fatigue tests of the matrix alloy and CCM analyses indicated this response was associated with stress relaxation of the matrix in the composite and subsequent load shedding to the fibers.

Gayda, John↗

NASA NTRS1991

Architecture and design of a 500-MHz gallium-arsenide processing element for a parallel supercomputer

The design of the processing element of GASP, a GaAs supercomputer with a 500-MHz instruction issue rate and 1-GHz subsystem clocks, is presented. The novel, functionally modular, block data flow architecture of GASP is described. The architecture and design of a GASP processing element is then presented. The processing element (PE) is implemented in a hybrid semiconductor module with 152 custom GaAs ICs of eight different types. The effects of the implementation technology on both the system-level architecture and the PE design are discussed. SPICE simulations indicate that parts of the PE are capable of being clocked at 1 GHz, while the rest of the PE uses a 500-MHz clock. The architecture utilizes data flow techniques at a program block level, which allows efficient execution of parallel programs while maintaining reasonably good performance on sequential programs. A simulation study of the architecture indicates that an instruction execution rate of over 30,000 MIPS can be attained with 65 PEs.

Fouts, Douglas J.↗