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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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NASA NTRS1993

High-performance compression of astronomical images

Astronomical images have some rather unusual characteristics that make many existing image compression techniques either ineffective or inapplicable. A typical image consists of a nearly flat background sprinkled with point sources and occasional extended sources. The images are often noisy, so that lossless compression does not work very well; furthermore, the images are usually subjected to stringent quantitative analysis, so any lossy compression method must be proven not to discard useful information, but must instead discard only the noise. Finally, the images can be extremely large. For example, the Space Telescope Science Institute has digitized photographic plates covering the entire sky, generating 1500 images each having 14000 x 14000 16-bit pixels. Several astronomical groups are now constructing cameras with mosaics of large CCD's (each 2048 x 2048 or larger); these instruments will be used in projects that generate data at a rate exceeding 100 MBytes every 5 minutes for many years. An effective technique for image compression may be based on the H-transform (Fritze et al. 1977). The method that we have developed can be used for either lossless or lossy compression. The digitized sky survey images can be compressed by at least a factor of 10 with no noticeable losses in the astrometric and photometric properties of the compressed images. The method has been designed to be computationally efficient: compression or decompression of a 512 x 512 image requires only 4 seconds on a Sun SPARCstation 1. The algorithm uses only integer arithmetic, so it is completely reversible in its lossless mode, and it could easily be implemented in hardware for space applications.

White, Richard L.↗
NASA NTRS1992

Cortical localization of cognitive function by regression of performance on event-related potentials

This paper demonstrates a new method of mapping cortical localization of cognitive function, using electroencephalographic data. Cross-subject regression analyses are used to identify cortical sites and post-stimulus latencies where there is a high correlation between subjects' performance and their cognitive event-related potential amplitude. The procedure was tested using a mental arithmetic task and was found to identify essentially the same cortical regions that have been associated with such tasks on the basis of research with patients suffering localized cortical lesions. Thus, it appears to offer an inexpensive, noninvasive tool for exploring the dynamics of localization in neurologically normal subjects.

Montgomery, R. W.↗
NASA NTRS1993

Dynamic programming on a shared-memory multiprocessor

Three new algorithms for solving dynamic programming problems on a shared-memory parallel computer are described. All three algorithms attempt to balance work load, while keeping synchronization cost low. In particular, for a multiprocessor having p processors, an analysis of the best algorithm shows that the arithmetic cost is O(n-cubed/6p) and that the synchronization cost is O(absolute value of log sub C n) if p much less than n, where C = (2p-1)/(2p + 1) and n is the size of the problem. The low synchronization cost is important for machines where synchronization is expensive. Analysis and experiments show that the best algorithm is effective in balancing the work load and producing high efficiency.

Edmonds, Phil↗
NASA NTRS1993

A new parallel-vector finite element analysis software on distributed-memory computers

A new parallel-vector finite element analysis software package MPFEA (Massively Parallel-vector Finite Element Analysis) is developed for large-scale structural analysis on massively parallel computers with distributed-memory. MPFEA is designed for parallel generation and assembly of the global finite element stiffness matrices as well as parallel solution of the simultaneous linear equations, since these are often the major time-consuming parts of a finite element analysis. Block-skyline storage scheme along with vector-unrolling techniques are used to enhance the vector performance. Communications among processors are carried out concurrently with arithmetic operations to reduce the total execution time. Numerical results on the Intel iPSC/860 computers (such as the Intel Gamma with 128 processors and the Intel Touchstone Delta with 512 processors) are presented, including an aircraft structure and some very large truss structures, to demonstrate the efficiency and accuracy of MPFEA.

Qin, Jiangning↗
NASA NTRS1993

A parallel algorithm for computing the eigenvalues of a symmetric tridiagonal matrix

A parallel algorithm, called polysection, is presented for computing the eigenvalues of a symmetric tridiagonal matrix. The method is based on a quadratic recurrence in which the characteristic polynomial is constructed on a binary tree from polynomials whose degree doubles at each level. Intervals that contain exactly one zero are determined by the zeros of polynomials at the previous level which ensures that different processors compute different zeros. The signs of the polynomials at the interval endpoints are determined a priori and used to guarantee that all zeros are found. The use of finite-precision arithmetic may result in multiple zeros; however, in this case, the intervals coalesce and their number determines exactly the multiplicity of the zero. For an N x N matrix the eigenvalues can be determined in O(log-squared N) time with N-squared processors and O(N) time with N processors. The method is compared with a parallel variant of bisection that requires O(N-squared) time on a single processor, O(N) time with N processors, and O(log N) time with N-squared processors.

Swarztrauber, Paul N.↗
NASA NTRS1993

Triangular spectral elements for incompressible fluid flow

We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility and are better conditioned and more accurate than quadrilateral elements when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied to the Poisson equation and are validated. The triangular discretizations are then applied to the incompressible Navier-Stokes equations, and a laminar channel flow solution is given. The new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.

Mavriplis, Catherine↗
NASA NTRS1923

Determination of climbing ability

The vertical distribution of the pressure, temperature, and density of the atmosphere varies from day to day. Thus, rates of climb on different days cannot be compared directly, but must be corrected with reference to a standard rate of diminution of air density with increasing altitude. The following problem, therefore, has to be solved. An airplane has climbed on a certain day under prevailing atmospheric conditions as shown by the barograph. How would the same airplane climb in a standard atmosphere? This problem has already been dealt with by Everling, using the monthly and yearly mean of the vertical temperature distribution. Von Mises solved the problem by arithmetical methods. Here, conditions are examined which shorten or lengthen the climbing time. In establishing the corrected barogram, computation seems more practical than graphical treatment. The basis of the answer to the question answered here is summed up in the remark that lift, drag, propeller thrust, and torque and engine power depend only on the density of the air and do not change with the pressure and temperature, provided that the density remains constant.

Blasius, H↗
NASA NTRS1954

Average Skin-Friction Drag Coefficients from Tank Tests of a Parabolic Body of Revolution (NACA RM-10)

Average skin-friction drag coefficients were obtained from boundary-layer total-pressure measurements on a parabolic body of revolution (NACA rm-10, basic fineness ratio 15) in water at Reynolds numbers from 4.4 x 10(6) to 70 x 10(6). The tests were made in the Langley tank no. 1 with the body sting-mounted at a depth of two maximum body diameters. The arithmetic mean of three drag measurements taken around the body was in good agreement with flat-plate results, but, apparently because of the slight surface wave caused by the body, the distribution of the boundary layer around the body was not uniform over part of the Reynolds number range.

Mottard, Elmo J↗
NASA NTRS1994

Coding For Compression Of Low-Entropy Data

Improved method of encoding digital data provides for efficient lossless compression of partially or even mostly redundant data from low-information-content source. Method of coding implemented in relatively simple, high-speed arithmetic and logic circuits. Also increases coding efficiency beyond that of established Huffman coding method in that average number of bits per code symbol can be less than 1, which is the lower bound for Huffman code.

Yeh, Pen-Shu↗
NASA NTRS1994

Algorithm For Integer Cosine Transforms

Algorithm computes coefficients of integer cosine transforms, containing only integer coefficients approximately proportional to floating-point coefficients of discrete cosine transforms. Used in compression of image data in blocks of N x N pixels, discrete cosine transforms involve large amounts of computation, typically amounting to 80 percent of computational load in data-compression scheme. In constructing integer approximations, competing requirements are to obtain data-compression and data-decompression performances comparable to those of corresponding descrete cosine transforms while taking advantage of simplicity afforded by integer arithmetic to reduce complexity and amount of computation.

Pollara, Fabrizio↗
NASA NTRS1994

Fast, Massively Parallel Data Processors

Proposed fast, massively parallel data processor contains 8x16 array of processing elements with efficient interconnection scheme and options for flexible local control. Processing elements communicate with each other on "X" interconnection grid with external memory via high-capacity input/output bus. This approach to conditional operation nearly doubles speed of various arithmetic operations.

Heaton, Robert A.↗
NASA NTRS1986

Chopped molecular beam multiplexing system

The integration of a chopped molecular beam mass spectrometer with a time multiplexing system is described. The chopping of the molecular beam is synchronized with the time intervals by a phase detector and a synchronous motor. Arithmetic means are generated for phase shifting the chopper with respect to the multiplexer. A four channel amplifier provides the capacity to independently vary the baseline and amplitude in each channel of the multiplexing system.

Adams, Billy R.↗
NASA NTRS1992

Formally biorthogonal polynomials and a look-ahead Levinson algorithm for general Toeplitz systems

Systems of linear equations with Toeplitz coefficient matrices arise in many important applications. The classical Levinson algorithm computes solutions of Toeplitz systems with only O(n(sub 2)) arithmetic operations, as compared to O(n(sub 3)) operations that are needed for solving general linear systems. However, the Levinson algorithm in its original form requires that all leading principal submatrices are nonsingular. An extension of the Levinson algorithm to general Toeplitz systems is presented. The algorithm uses look-ahead to skip over exactly singular, as well as ill-conditioned leading submatrices, and, at the same time, it still fully exploits the Toeplitz structure. In our derivation of this algorithm, we make use of the intimate connection of Toeplitz matrices with formally biorthogonal polynomials.

Freund, Roland W.↗
NASA NTRS1993

SLR data screening; location of peak of data distribution

At the 5th Laser Ranging Instrumentation Workshop held at Herstmonceux in 1984, consideration was given to the formation of on-site normal points by laser stations, and an algorithm was formulated. The algorithm included a recommendation that an iterated 3.0 x rms rejection criterion should be used to screen the data, and that arithmetic means should be formed within the normal point bins of the retained data. From Sept. 1990 onwards, this algorithm and screening criterion have been brought into effect by various laser stations for forming on-site normal points, and small variants of the algorithm are used by most analysis centers for forming normal points from full-rate data, although the data screening criterion they use ranges from about 2.5 to 3.0 x rms. At the CSTG Satellite Laser Ranging (SLR) Subcommission, a working group was set up in Mar. 1991 to review the recommended screening procedure. This paper has been influenced by the discussions of this working group, although the views expressed are primarily those of this author. The main thrust of this paper is that, particularly for single photon systems, a more important issue than data screening is the determination of the peak of a data distribution and hence, the determination of the bias of the peak from the mean. Several methods of determining the peak are discussed.

Sinclair, Andrew T.↗
NASA NTRS1991

VLSI architectures for geometrical mapping problems in high-definition image processing

This paper explores a VLSI architecture for geometrical mapping address computation. The geometric transformation is discussed in the context of plane projective geometry, which invokes a set of basic transformations to be implemented for the general image processing. The homogeneous and 2-dimensional cartesian coordinates are employed to represent the transformations, each of which is implemented via an augmented CORDIC as a processing element. A specific scheme for a processor, which utilizes full-pipelining at the macro-level and parallel constant-factor-redundant arithmetic and full-pipelining at the micro-level, is assessed to produce a single VLSI chip for HDTV applications using state-of-art MOS technology.

Kim, K.↗
NASA NTRS1993

Are the C delta light nitrogen and noble gases located in the same carrier?

Light nitrogen and the HL family noble gas components of C(sub delta) appear to be separable by high resolution pyrolysis experiments. Thus C(sub delta) is not a homogeneous material and probably consists of debris of many stars. The question of whether the N and Xe(HL) actually reside in different carriers continues to be addressed. It is well known that C(sub delta) which was identified as nanometer sized diamonds contains isotopically anamalous elements, in particular noble gases including Xe(HL) and its family and light nitrogen (delta(N-15) down to -350 percent). Before the true nature of C(sub delta) was recognized, it was easy to suppose that the Xe(HL) and light nitrogen were located in the same carrier. However, recognition that light nitrogen in diamond from different samples varies by greater than a factor of six compared to Xe(HL) fluctuations of ca. 20 percent makes such an assumption questionable. On the basis of simple arithmetic logic, the Xe and nitrogen cannot be absolutely co-located. The average diamond grain consists of only about 1000-2000 atoms of carbon; one grain among a few x 10(exp 6) contains an atom of Xe(HL) while 5-30 atoms of light nitrogen are the typical number which need to be in every diamond grain to account for observed concentrations. If some grains are devoid of N, the others have to have a higher N concentration. Even if we were able to analyze an individual grain of the diamond for noble gases and nitrogen, we would be faced with the monumental task of locating the one amongst 10(exp 6) identical grains containing the Xe atom to examine its nitrogen content. The problem can be simplified to some extent if instead of Xe, He which is 10(exp 4) times more abundant is assumed to be a member of the HL family. Attempts to fractionate the separate carriers might be attempted using He and N as guiding indicators but even experiments of this nature are for the future. Faced with apparently insoluble problems, we have returned to an investigation we last used in our original efforts to find isotopically light nitrogen, that is to compare release patterns of the different components during stepped pyrolysis and combustion.

Verchovsky, A. B.↗
NASA NTRS1993

Correctness properties for iterated hardware structures

Iterated structures occur frequently in hardware. This paper describes properties required of mathematical relations that can be implemented iteratively and demonstrates the use of these properties on a generalized class of adders. This work provides a theoretical basis for the correct synthesis of iterated arithmetic structures.

Windley, Phillip J.↗