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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Characteristic microwave background distortions from collapsing domain wall bubbles

The magnitude and angular pattern of distortions of the microwave background are analyzed by collapsing spherical domain walls. A characteristic pattern of redshift distortions of red or blue spikes surrounded by blue discs was found. The width and height of a spike is related to the diameter and magnitude of the disc. A measurement of the relations between these quantities thus can serve as an unambiguous indicator for a collapsing spherical domain wall. From the redshift distortion in the blue discs an upper bound was found on the surface energy density of the walls sigma is less than or approximately 8 MeV cubed.

Goetz, Guenter↗
NASA NTRS1989

Biaxial constitutive modelling and testing of a single crystal superalloy at elevated temperatures

A viscoplastic constitutive model for single crystal superalloys is developed from crystallographic slip theory. The model is applied to the tension and torsion deformation behavior of the single crystal superalloy PWA 1480 at 871 C (1600 F). Both octahedral and cube slip behavior are needed to model the deformation behavior of single crystal superalloys at elevated temperature.

Walker, K. P.↗
NASA NTRS1990

Galaxy formation and the origin of the ionizing flux at large redshift

The absence of any continuous Ly-alpha opacity from the intergalactic medium at z = 3-4.5 can be understood if a significant population of star-forming galaxies is present at these redshifts. It is shown that such galaxies can be present within the galaxy populations at B = 22 to 27. The expected ionization produced during galaxy formation is analyzed in terms of highly model-independent metal production arguments and it is concluded that (if such galaxies are dust-free and transparent to ionizing photons) then at least 4(H0/50 km/s Mpc)-cubed percent of galaxy formation would have to have occurred in this redshift range.

Songaila, A.↗
NASA NTRS1990

Coarsening in binary solid-liquid mixtures

A theory of Ostwald ripening has been developed for a solid-liquid mixture cosisting of a low volume fraction array of spherical solid particles in a liquid wherein the coarsening process proceeds via the transport of both heat and mass. It is found that the simultaneous transport of heat and mass during ripening does not alter the exponents of the temporal power laws governing the ripening process from their classical values but does alter the amplitudes of these power laws. The growth rate of the cube of the average particle radius, the rate constant, is found to depend both on the alloy solute concentration and the ratio of the thermal to solutal diffusivities. In most metallic systems, a large decrease in the rate constant can be expected with small additions of solute to a pure metal. Possible extensions of this theory to the analogous problem of ripening in isothermal ternary alloys are also discussed.

Voorhees, P. W.↗
NASA NTRS1989

Opposed-flow flame spread and extinction in mixed-convection boundary layers

Experimental data for flame spread down thin fuel samples in an opposing, mixed-convection, boundary-layer flow are analyzed to determine the gas-phase velocity that characterizes how the flame reacts as it spreads toward the leading edge of the fuel sample into a thinning boundary layer. In the forced-flow limit where the cube of the Reynolds number divided by the Grashof number, Re exp 3/Gr, is large, L(q)/L(e), where L(q) is a theoretical flame standoff distance at extinction and L(e) is the measured distance from the leading edge of the sample where extinction occurs, is found to be proportional to Re exp n with n = -0.874 and Re based on L(e). The value of n is established by the character of the flow field near the leading edge of the flame. The Re dependence is used, along with a correction for the mixed-convection situation where Re exp 3/Gr is not large, to construct a Damkohler number with which the measured spread rates correlate for all values of Re exp 3/Gr.

Altenkirch, R. A.↗
NASA NTRS1990

Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise

Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering-gallery sapphire ring resonator with Q of 200,000. This mode involves little metallic conduction and allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified, in good agreement with frequency calculations. For a 5-cm wheel resonator in a 7.6-cm container, Q values above 100,000 were found at room temperature for all of the modes in this sequence. Coupling Q-values for these same modes ranged from 10,000 (n = 5) to 100,000 (n = 10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n = 10 (7.84-GHz) mode showed a 1/f cubed dependence for low offset frequencies, and a value of L(f) = -55 dB/Hz at an offset of 10 Hz from the carrier.

Dick, G. John↗
NASA NTRS1990

Volumetric imaging of space debris using sun microsystem's TAAC-1 application accelerator board

Analysis of space debris requires the researcher to have a three-dimensional spatial framework and understanding. By using computers to image and display the space debris volumes, the researcher is provided with an added visual analysis tool. This paper describes volumetric visualization of space debris. Two imaging approaches are used. The first method visualizes the cube faces of the volumetric image. The second method uses a ray-tracing technique to display surfaces within the volume. Three examples of space debris volumes are described.

Luetkemeyer, Kelly G.↗
NASA NTRS1991

Conical Mirrors For Quasi-Retroreflection

Single and multiple-nested conical mirrors assembled and positioned to provide several distinct orders of retroreflection. Design and orientation of "cones" determines positions of, and solid angles subtended by discrete orders of retroreflection. Accommodates larger range of incident angles than corner-cube reflectors. Also provides greater spectral coverage than conventional lens-and mirror retroreflectors. Potential applications include interferometry, metrology, lasers, position and motion sensors, instrument test and calibration, and expanded capability of highway markers and signs.

Dekany, Richard G.↗
NASA NTRS1990

Multiple axis reticle

A reticle permits the alignment of three orthogonal axes (X, Y and Z) that intersect at a common target point. Thin, straight filaments are supported on a frame. The filaments are each contained in a different orthogonal plane (S sub xy, S sub xz, and S sub yz) and each filament intersects two of the three orthogonal axes. The filaments, as viewed along the frame axis, give the appearance of a triangle with a V extending from each triangle vertex. When axial alignment is achieved, the filament portions adjacent to a triangle vertex are seen (along the axis of interest) as a right-angle cross, whereas these filament portions are seen to intersect at an oblique angle when axial misalignment occurs. The reticle is open in the region near the target point leaving ample space for alignment aids such as a pentaprism or a cube mirror.

Barns, Chris E.↗
NASA NTRS1991

Complete exchange on the iPSC-860

The implementation of complete exchange on the circuit switched Intel iPSC-860 hypercube is described. This pattern, also known as all-to-all personalized communication, is the densest requirement that can be imposed on a network. On the iPSC-860, care needs to be taken to avoid edge contention, which can have a disastrous impact on communication time. There are basically two classes of algorithms that achieve contention-free complete exchange. The first contains the classical standard exchange algorithm that is generally useful for small message sizes. The second includes a number of optimal or near-optimal algorithms that are best for large messages. Measurement of communication overhead on the iPSC-860 are given and a notation for analyzing communication link usage is developed. It is shown that for the two classes of algorithms, there is substantial variation in performance with synchronization technique and choice of message protocol. Timings of six implementations are given; each of these is useful over a particular range of message size and cube dimension. Since the complete exchange is a superset of communication patterns, these timings represent upper bounds on the time required by an arbitrary communication requirement. These results indicate that the programmer needs to evaluate several possibilities before finalizing an implementation - a careful choice can lead to very significant savings in time.

Bokhari, Shahid H.↗
NASA NTRS1991

Multiphase complete exchange on a circuit switched hypercube

On a distributed memory parallel computer, the complete exchange (all-to-all personalized) communication pattern requires each of n processors to send a different block of data to each of the remaining n - 1 processors. This pattern is at the heart of many important algorithms, most notably the matrix transpose. For a circuit switched hypercube of dimension d(n = 2(sup d)), two algorithms for achieving complete exchange are known. These are (1) the Standard Exchange approach that employs d transmissions of size 2(sup d-1) blocks each and is useful for small block sizes, and (2) the Optimal Circuit Switched algorithm that employs 2(sup d) - 1 transmissions of 1 block each and is best for large block sizes. A unified multiphase algorithm is described that includes these two algorithms as special cases. The complete exchange on a hypercube of dimension d and block size m is achieved by carrying out k partial exchange on subcubes of dimension d(sub i) Sigma(sup k)(sub i=1) d(sub i) = d and effective block size m(sub i) = m2(sup d-di). When k = d and all d(sub i) = 1, this corresponds to algorithm (1) above. For the case of k = 1 and d(sub i) = d, this becomes the circuit switched algorithm (2). Changing the subcube dimensions d, varies the effective block size and permits a compromise between the data permutation and block transmission overhead of (1) and the startup overhead of (2). For a hypercube of dimension d, the number of possible combinations of subcubes is p(d), the number of partitions of the integer d. This is an exponential but very slowly growing function and it is feasible over these partitions to discover the best combination for a given message size. The approach was analyzed for, and implemented on, the Intel iPSC-860 circuit switched hypercube. Measurements show good agreement with predictions and demonstrate that the multiphase approach can substantially improve performance for block sizes in the 0 to 160 byte range. This range, which corresponds to 0 to 40 floating point numbers per processor, is commonly encountered in practical numeric applications. The multiphase technique is applicable to all circuit-switched hypercubes that use the common e-cube routing strategy.

Bokhari, Shahid H.↗
NASA NTRS1991

The environment workbench: A design tool for Space Station Freedom

The environment workbench (EWB) is being developed for NASA by S-CUBED to provide a standard tool that can be used by the Space Station Freedom (SSF) design and user community for requirements verification. The desktop tool will predict and analyze the interactions of SSF with its natural and self-generated environments. A brief review of the EWB design and capabilities is presented. Calculations using a prototype EWB of the on-orbit floating potentials and contaminant environment of SSF are also presented. Both the positive and negative grounding configurations for the solar arrays are examined to demonstrate the capability of the EWB to provide quick estimates of environments, interactions, and system effects.

Jongeward, Gary A.↗
NASA NTRS1990

Fabry-Perot observations of comet Austin

Preliminary results of a program to observe Comet Austin (1990c1) from 16 April to 4 May and from 11 May to 27 May 1990 using the West Auxiliary of the McMath Solar Telescope on Kitt Peak, Arizona were presetned. The observations were made with a 15 cm duel-etalon Fabry-Perot scanning and imaging spectrometer with two modes of operation: a high resolution mode with a velocity resolution of 1.2 km/s and a medium resolution mode with a velocity resolution 10 km/s. Scanning data was obtained with an RCA C31034A photomultiplier tube and imaging data was obtained with a Photometrics LN2 cooled CCD camera with a 516 by 516 Ford chip. The results include: (1) information on the coma outflow velocity from high resolution spectral profiles of (OI)6300 and NH2 emissions, (2) gaseous water production rates from medium resolution observation of (OI)6300, (3) spectra of H2O(+) emissions in order to study the ionized component of the coma, (4) spatial distribution of H2O(+) emission features from sequences of velocity resolved images (data cubes), and (5) spatial distribution of (OI)6300 and NH2 emissions from medium resolution images. The field of view on the sky was 10.5 arcminutes in diameter. In the imaging mode the CCD was binned 4 by 4 resulting in 7.6 sec power pixel and a subarray readout for a field of view of 10.5 min.

Schultz, David↗
NASA NTRS1991

Fuzzy associative memories

Mappings between fuzzy cubes are discussed. This level of abstraction provides a surprising and fruitful alternative to the propositional and predicate-calculas reasoning techniques used in expert systems. It allows one to reason with sets instead of propositions. Discussed here are fuzzy and neural function estimators, neural vs. fuzzy representation of structured knowledge, fuzzy vector-matrix multiplication, and fuzzy associative memory (FAM) system architecture.

Kosko, Bart↗
NASA NTRS1991

Effect of Li level, artificial aging, and TiB2 reinforcement on the modulus of Weldalite (tm) 049

The dynamic Young's Modulus (E) was determined for (1) alloys 049(1.3)(heat 072), (2) 049(1.9), and (3) 049(1.3) TiB2 in the T3 temper and after aging at 160 C were made on a single 0.953 cm (0.375 in) cube to reduce scatter from microstructural inhomogeneities. Both shear and transverse wave velocities were measured for the L, LT, and ST directions by a pulse echo technique. These velocities were then used to calculate modulus. The change is shown in E with aging time at 160 C (320 F) for the three alloys. It is clear from the plots that aging has a minor, but measurable, influence on the E of alloys 049(1.3) and 049(1.9): E decreases by -2.5 pct. for 2 and 3 during the initial stages of artificial aging. This decrease in E generally follows the strength reversion. On further aging beyond the reversion well, E increases and then decreases again as the alloy overage. The slightly higher modulus in the T8 than in the T3 temper is consistent with the presence of the high modulus T sub 1 phase in the T8 temper. A similar change in E was observed on aging for the TiB2 reinforced variant that also follows the aging curve.

Source record↗
NASA NTRS1990

Development of a sensor coordinated kinematic model for neural network controller training

A robotic benchmark problem useful for evaluating alternative neural network controllers is presented. Specifically, it derives two camera models and the kinematic equations of a multiple degree of freedom manipulator whose end effector is under observation. The mapping developed include forward and inverse translations from binocular images to 3-D target position and the inverse kinematics of mapping point positions into manipulator commands in joint space. Implementation is detailed for a three degree of freedom manipulator with one revolute joint at the base and two prismatic joints on the arms. The example is restricted to operate within a unit cube with arm links of 0.6 and 0.4 units respectively. The development is presented in the context of more complex simulations and a logical path for extension of the benchmark to higher degree of freedom manipulators is presented.

Jorgensen, Charles C.↗
NASA NTRS1990

A kinematic determination of the structure of the double ring planetary nebula NGC 2392, the Eskimo

Slit spectra and existing 'velocity cube' data have been used to determine the structure of the double ring PN NGC 2392. The inner shell is a stellar wind-sculpted prolate spheroid with a ratio of axes of 2:1 and the approaching end of the long axis pointed 20 deg from the line of sight in P.A. = 200 deg. The outer ring is caused by an outer disk with density dropping off with distance from the central star and with distance from its plane, which is the same as the equatorial band of high density in the inner shell. The outer disk contains a ring of higher density knots at a distance of 16 arcsec and is losing material through free expansion, forming an outer envelope of increasing velocity. Forbidden S II spectra are used to determine the densities in all of the major regions of the nebula. It is argued that the filamentary cores at the centers of the knots seen in the outer ring originate in the sublimation of bodies formed at the same time as the parent star.

O'Dell, C. R.↗
NASA NTRS1990

Application of implicit numerical techniques to the solution of the three-dimensional diffusion equation

Implicit techniques for calculating three-dimensional, time-dependent heat diffusion in a cube are tested with emphasis on storage efficiency, accuracy, and speed of calculation. For this purpose, a tensor product technique with both Chebyshev collocation and finite differences and a generalized conjugate gradient technique with finite differences are used in conjunction with Crank-Nicolson discretization. An Euler explicit finite difference calculation is performed for use as a benchmark. The implicit techniques are found to be competitive with the Euler explicit method in terms of storage efficiency and speed of calculation and offer advantages both in accuracy and stability. Mesh stretching in the finite difference calculations is shown to markedly improve the accuracy of the solution.

Peltier, Leonard Joel↗