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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,297 records · Page 72

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NASA NTRS1972

The computation of optimal control programmes using a modified successive sweep method.

A second-order method for numerically solving control optimization problems has been developed. The method, referred to as the modified sweep method (MSM), differs from the successive sweep method (SSM) proposed by McReynolds and Bryson (1965) in that the conditions for local control optimality are used to determine the control as an explicit function of the state variables and time. The control is eliminated from the problem and the solution to the resulting two-point boundary value problem can be obtained by linear perturbation methods. The modified sweep method proposed here uncouples the perturbation equations for the state variables and the Lagrange multipliers by using a generalized matrix-Riccati transformation of variables. The resulting algorithm for the numerical iteration process is concerned with determining the initial values of a set of Lagrange multipliers rather than correcting a numerical control programme over the entire time interval of interest.

Colunga, D.↗

NASA NTRS1972

One-phonon transitions observed in the scattering of He atoms from a LiF/001/ surface.

For the scattering of a nearly monoenergetic beam of thermal-energy He atoms from a cleaved (001)LiF crystal surface, speed distributions of the reflected atoms are measured at suitably spaced scattering angles within the plane of incidence. From the measurements, elastic and one-phonon inelastic scattering processes are identified. Elastically scattered atoms distribute themselves in a set of sharp diffraction peaks. One-phonon inelastically scattered atoms are dispersed about each diffraction peak. The most probable velocities of the inelastically scattered atoms exhibit a characteristic sawtooth variation with scattering angle which, to first approximation, corresponds to conservation of the component of atom momentum tangent to the surface.-

Fisher, S. S.↗

NASA NTRS1971

The Mariner 6 and 7 pictures of Mars

A comprehensive set of high quality reproductions of the final, computer-processed television pictures of Mars is presented. The genesis and unique characteristics of the pictures are explained, interesting features are pointed out, and some indication of their significance in the history of Mars investigations is provided.

Collins, S. A., Jr.↗

NASA NTRS1974

Nonproportional loading limit for structures

The design of most structures involves ensuring integrity for several independent loading conditions. Often, it is rational to design these, exploiting the ductility of the materials to reduce structural costs. Then, ensuring integrity evokes the need for nonmonotonic limit analyses. A groundwork is laid for implementing these analyses. An alternate limit load characterization to that of Greenberg is provided, a mathematical statement of the problem leading to both monotonic (proportional) and nonmonotonic limit loads values is formulated, a direct limit load analysis procedure for analysis within a finite-element framework is described, and limit loads for sets of simple structures are evaluated. A direct limit analysis process is described, and monotonic limit loads are characterized. The process furnishes 'exact' values of limit loads with increasing efficiency as the number of structural elements and force redundancy decreases. Tests show that the accuracy of predicting nonmonotonic limit loads is very sensitive to the number of degrees of freedom in the analysis compared with the total number in the model.

Melosh, R. J.↗

NASA NTRS1975

UHMLE: Program description user guide

A program which computes maximum likelihood estimates for the general normal mixture is introduced. The program allows the user to fix any subsets of the mixture parameters; this fixed set may be redefined at various times in the iteration process. There is considerable time saved in computing the likelihoods if the diagonal form is specified. Hence, in the early iterations the diagonal assumption might be used, changing over to the full covariance mode later in the iteration process for a more refined solution. This flexibility allows the user to choose the sequence of parameter configurations in the iteration process which he feels will optimize the computation time required as well as possibly avoid convergence to suboptimal local maxima of the likelihood function.

Cobely, W. A.↗

NASA NTRS1976

Onboard Experiment Data Support Facility

An onboard array structure has been devised for end to end processing of data from multiple spaceborne sensors. The array constitutes sets of programmable pipeline processors whose elements perform each assigned function in 0.25 microseconds. This space shuttle computer system can handle data rates from a few bits to over 100 megabits per second.

Source record↗

NASA NTRS1977

General purpose film plotting system

The general purpose film plotting system which is a plot program design to handle a majority of the data tape formats presently available under OS/360 was discussed. The convenience of this program is due to the fact that the user merely describes the format of his data set and the type of data plots he desires. It processes the input data according to the given specifications. The output is generated on a tape which yields data plots when processed by the selected plotter. A summary of each job is produced on the printer.

Mcquillan, C.↗

NASA NTRS1977

Landsat digital data application to forest vegetation and land use classification in Minnesota

Landsat digital data were used to map eleven categories of land cover in north central Minnesota. The classification accuracy of these maps was found to be very low and they were not adequate for use by field level resource managers. A discussion of the advantages and disadvantages of various processing systems, different algorithms, and the problems in selecting training sets, is included.

Mead, R. A.↗

NASA NTRS1980

Azimuth correlator design for IC chip

Azimuth correlator circuit synthetic-aperature radar (SAR) is designed for single integrated circuit (IC) chip. Azimuth correlator modules constructed with sets of such chips could make real-time signal processing possible. Primary advantages are realized in areas of weight and power requirement reductions.

Tyree, V. C.↗

NASA NTRS1979

Phased models for evaluating the performability of computing systems

A phase-by-phase modelling technique is introduced to evaluate a fault tolerant system's ability to execute different sets of computational tasks during different phases of the control process. Intraphase processes are allowed to differ from phase to phase. The probabilities of interphase state transitions are specified by interphase transition matrices. Based on constraints imposed on the intraphase and interphase transition probabilities, various iterative solution methods are developed for calculating system performability.

Wu, L. T.↗

NASA NTRS1980

Social issues and implications of remote sensing applications: Paradigms of technology transfer

The transfer of technology from one federal agency to another was observed in the case of the move of LANDSAT to NOAA. An array of unanticipated consequences was found that have important impacts on both the process and outcome of the transfer. When the process was studied from viewpoint of the ultimate recipient, a set of expectations and perceptions were found that figure more in a final assessment than do the attributes of the technology being transfered. The question of how to link a technology with a community of potential users was studed in detail.

Hoos, I. R.↗

NASA NTRS1983

Ambiguities in spaceborne synthetic aperture radar systems

An examination of aspects of spaceborne SAR time delay and Doppler ambiguities has led to the formulation of an accurate method for the evaluation of the ratio of ambiguity intensities to that of the signal, which has been applied to the nominal SAR system on Seasat. After discussing the variation of this ratio as a function of orbital latitude and attitude control error, it is shown that the detailed range migration-azimuth phase history of an ambiguity is different from that of a signal, so that the images of ambiguities are dispersed. Seasat SAR dispersed images are presented, and their dispersions are eliminated through an adjustment of the processing parameters. A method is also presented which uses a set of multiple pulse repetition sequences to determine the Doppler centroid frequency absolute values for SARs with high carrier frequencies and poor attitude measurements.

Li, F. K.↗

NASA NTRS1982

Life sciences flight experiments program mission science requirements document. The first life sciences dedicated Spacelab mission, part 1

The Mission Science Requirements Document (MSRD) for the First Dedicated Life Sciences Mission (LS-1) represents the culmination of thousands of hours of experiment selection, and science requirement definition activities. NASA life sciences has never before attempted to integrate, both scientifically and operationally, a single mission dedicated to life sciences research, and the complexity of the planning required for such an endeavor should be apparent. This set of requirements completes the first phase of a continual process which will attempt to optimize (within available programmatic and mission resources) the science accomplished on this mission.

Rummel, J. A.↗

NASA NTRS1987

Particle simulation of plasmas on the massively parallel processor

Particle simulations, in which collective phenomena in plasmas are studied by following the self consistent motions of many discrete particles, involve several highly repetitive sets of calculations that are readily adaptable to SIMD parallel processing. A fully electromagnetic, relativistic plasma simulation for the massively parallel processor is described. The particle motions are followed in 2 1/2 dimensions on a 128 x 128 grid, with periodic boundary conditions. The two dimensional simulation space is mapped directly onto the processor network; a Fast Fourier Transform is used to solve the field equations. Particle data are stored according to an Eulerian scheme, i.e., the information associated with each particle is moved from one local memory to another as the particle moves across the spatial grid. The method is applied to the study of the nonlinear development of the whistler instability in a magnetospheric plasma model, with an anisotropic electron temperature. The wave distribution function is included as a new diagnostic to allow simulation results to be compared with satellite observations.

Gledhill, I. M. A.↗

NASA NTRS1987

A study of carbon monoxide distribution determinations for a global transport model

A system of programs which model the chemistry and transport of carbon monoxide and methane in the Earth's atmosphere on a global scale was installed onto the NASA-Langley central scientific computer network. This system, the GLOBAL system, consists of a user-friendly set of procedural files which allow for simplified pre-processing, execution, and post-processing for all program elements. The package includes procedures for obtaining the NMC meteorological data, calculating the vertical winds to satisfy mass conservation, determining the boundary layer, and executing the transport/chemical model for carbon monoxide. In addition, plotting, saving to tape, and reading from tape routines were developed. Final modifications to the subprograms for processing the input data for the transport/chemistry model have improved these data to more accurately reflect true atmospheric conditions. The transfer of the transport/chemistry model from the NCAR CRAY system to the NASA-Langley VPS-32 system was completed. The problems encountered during this process and their resolutions are discussed.

Peters, Leonard K.↗

NASA NTRS1988

Adapting high-level language programs for parallel processing using data flow

EASY-FLOW, a very high-level data flow language, is introduced for the purpose of adapting programs written in a conventional high-level language to a parallel environment. The level of parallelism provided is of the large-grained variety in which parallel activities take place between subprograms or processes. A program written in EASY-FLOW is a set of subprogram calls as units, structured by iteration, branching, and distribution constructs. A data flow graph may be deduced from an EASY-FLOW program.

Standley, Hilda M.↗

NASA NTRS1989

Optical Firmware

Data-processing system exploits high speeds inherent in optical elements. Instruction sets for different computer operations reside on different external memory chips. Laser diodes activated for each operation generate light, reflected by holographic optical element to designated receptors in arithmetic and logic unit. Pattern of light beams embodies instruction set at given instant. With potential ability to reprogram in real time, conceptual system applicable to task-driven programming or artificial intelligence.

Bergman, Larry A.↗

NASA NTRS1989

Ideal Resampling Of Discrete Sequences

Spectral information preserved to extent possible. Technique developed to shrink or expand discrete input sequence of numbers into output sequence in manner preserving input spectrum up to Nyquist limit of smaller of two sequences. In case of expansion, technique also prevents introduction of spurious frequencies not present in input. While applicable to many kinds of data sampled at regular interval, particularly useful in processing and enhancement of images, where discrete sequences spatially ordered sets of picture-element brightness values. Image coarsened by resampling to reduce number of picture elements while preserving as much as possible of original image information. Used to generate intermediate images at small intervals between frames, thereby suppressing appearance of jerky motion caused by sudden jumps between frames at low frame rate.

Watson, Andrew B.↗