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NASA NTRS1985

Analysis of Nonvolatile Residue (NVR) from Spacecraft Systems

Organic contamination on critical spacecraft surfaces can cause electronic problems, serious attenuation of various optical signals, thermal control changes, and adhesion problems. Such contaminants can be detected early by the controlled use of witness mirrors, witness plates, wipe sampling, or direct solvent extraction. Each method requires careful control of variables of technique and materials to attain the ultimate sensitivities inherent to that procedure. Subsequent chemical analysis of the contaminant sample by infrared and mass spectrometry identifies the components, gives semiquantitative estimates of contaminant thickness, indicates possible sources of the nonvolatile residue (NVR), and provides guidance for effective cleanup procedures.

Colony, J. A.↗

NASA NTRS1985

Estimating the R-curve from residual strength data

A method is presented for estimating the crack-extension resistance curve (R-curve) from residual-strength (maximum load against original crack length) data for precracked fracture specimens. The method allows additional information to be inferred from simple test results, and that information can be used to estimate the failure loads of more complicated structures of the same material and thickness. The fundamentals of the R-curve concept are reviewed first. Then the analytical basis for the estimation method is presented. The estimation method has been verified in two ways. Data from the literature (involving several materials and different types of specimens) are used to show that the estimated R-curve is in good agreement with the measured R-curve. A recent predictive blind round-robin program offers a more crucial test. When the actual failure loads are disclosed, the predictions are found to be in good agreement.

Orange, T. W.↗

NASA NTRS1986

Residual stress measurements in carbon steel

External dc magnetic field-induced changes in natural velocity of Rayleigh surface waves were measured in steel specimens under various stress conditions. The low field slopes of curves representing the fractional changes of natural velocity were proved to provide correct stress information in steels with different metallurgical properties. The slopes of curves under uniaxial compression, exceeding about one third of the yield stress, fell below zero in all the specimens when magnetized along the stress axis. The slopes under tension varied among different steels but remained positive in any circumstances. The stress effect was observed for both applied and residual stress. A physical interpretation of these results is given based on the stress-induced domain structure changes and the delta epsilon effect. Most importantly, it is found that the influence of detailed metallurgical properties cause only secondary effects on the obtained stress information.

Heyman, J. S.↗

NASA NTRS1985

Preconditioned minimal residual methods for Chebyshev spectral calculations

The problem of preconditioning the pseudospectral Chebyshev approximation of an elliptic operator is considered. The numerical sensitiveness to variations of the coefficients of the operator are investigated for two classes of preconditioning matrices: one arising from finite differences, the other from finite elements. The preconditioned system is solved by a conjugate gradient type method, and by a Dufort-Frankel method with dynamical parameters. The methods are compared on some test problems with the Richardson method and with the minimal residual Richardson method.

Canuto, C.↗

NASA NTRS1985

Polynomic nonlinear dynamical systems - A residual sensitivity method for model reduction

The motivation for using polynomic combinations of system states and inputs to model nonlinear dynamics systems is founded upon the classical theories of analysis and function representation. A feature of such representations is the need to make available all possible monomials in these variables, up to the degree specified, so as to provide for the description of widely varying functions within a broad class. For a particular application, however, certain monomials may be quite superfluous. This paper examines the possibility of removing monomials from the model in accordance with the level of sensitivity displayed by the residuals to their absence. Critical in these studies is the effect of system input excitation, and the effect of discarding monomial terms, upon the model parameter set. Therefore, model reduction is approached iteratively, with inputs redesigned at each iteration to ensure sufficient excitation of remaining monomials for parameter approximation. Examples are reported to illustrate the performance of such model reduction approaches.

Yurkovich, S.↗

NASA NTRS1986

Preconditioned conjugate residual methods for the solution of spectral equations

Conjugate residual methods for the solution of spectral equations are described. An inexact finite-difference operator is introduced as a preconditioner in the iterative procedures. Application of these techniques is limited to problems for which the symmetric part of the coefficient matrix is positive definite. Although the spectral equation is a very ill-conditioned and full matrix problem, the computational effort of the present iterative methods for solving such a system is comparable to that for the sparse matrix equations obtained from the application of either finite-difference or finite-element methods to the same problems. Numerical experiments are shown for a self-adjoint elliptic partial differential equation with Dirichlet boundary conditions, and comparison with other solution procedures for spectral equations is presented.

Wong, Y. S.↗

NASA NTRS1986

Residual strength of five boron/aluminum laminates with crack-like notches after fatigue loading

Boron/aluminum specimens were made with crack-like slits in the center and with various proportions of 0 and + or - 45 deg plies. They were fatigue loaded and then fractured to determine their residual strengths. The fatigue loads were generally in the range of 60 to 80 percent of the static tensile strength of the specimen as determined from a previous study, and the stress ratio was .05. For virtually all of the specimens the fatigue loading was continued for 100,000 cycles. The specimens were radiographed after the fatigue loading to determine the nature of the fatigue damage. A few specimens were sectioned and examined in a scanning electron microscope after being radiographed in order to verify the interpretation of the radiographs and also to get a better insight into the nature of the fatigue damage. The results indicate that the fatiguing does not significantly affect the strength of the specimens tested. The results of the radiography and of the scanning electron microscopy indicate that the 45 deg plies suffer extensive damage in the form of split and broken fibers and matrix cracking in the vicinity of the ends of the split. By contrast, the only significant damage to the 0 deg plies was a single 0 deg matric crack growing from the ends of the slit and between the 0 deg fibers.

Simonds, R. A.↗

NASA NTRS1986

Wind-driven surface transport in stratified closed basins Direct versus residual circulations

The wind-driven circulation in a moderately large, stratified basin Lake Tahoe, California-Nevada, is studied using a numerical model. Direct circulations, in which the current directions remain relatively constant and the mean circulation formed over several days resembles the instantaneous circulation, and residual circulations, in which the currents fluctuate continuously and the mean circulation is characterized by small net displacements of parcels after large oscillations, are found. The lake's double gyre, dominated by the large anticyclonic northern gyre, differs from the single cyclonic gyre reported for other stratified basins, and examination of the modeled vorticity budget in the surface layer shows that the curl of the wind stress must be included to obtain the observed direct double gyre circulation.

Strub, P. T.↗

NASA NTRS1986

A new VLSI complex integer multiplier which uses a quadratic-polynomial residue system with Fermat numbers

A quadratic-polynomial Fermat residue number system (QFNS) has been used to compute complex integer multiplications. The advantage of such a QFNS is that a complex integer multiplication requires only two integer multiplications. In this article, a new type Fermat number multiplier is developed which eliminates the initialization condition of the previous method. It is shown that the new complex multiplier can be implemented on a single VLSI chip. Such a chip is designed and fabricated in CMOS-pw technology.

Truong, T. K.↗

NASA NTRS1986

The 14 month wind stressed residual circulation (pole tide) in the North Sea

From published research it is known that a quasi-periodic 14 month atmospheric pressure oscillation of a few tenths of a millibar exists in the region of the North and Baltic Seas. At some time in the cycle the associated wind stress has a westerly component that drives a circulation in the North Sea. The results of a dynamical model and comparisons with several North Sea residual circulation studies show that a large sea level gradient results along the Dutch coast. It is this feature that has been referred to as the enhanced pole tide. The dynamical similarity of this pole tide in the North and Baltic Seas to the annual and seasonal wind forced circulations is considered. It is inferred that the large deviations of the pole tide from equilibrium at coastal stations are the result of this sea level set up forces by the 14 month wind stress cycle.

Oconnor, W. P.↗

NASA NTRS1987

Rare earth patterns in shergottite phosphates and residues

Leaching experiments with 1M HCl on ALHA 77005 powder show that rare earth elements (REE) are concentrated in accessory phosphate phases (whitlockite, apatite) that govern the REE patterns of bulk shergottites. The REE patterns of whitlockite are typically light REE-depleted with a negative Eu anomaly and show a hump at the heavy REE side, while the REE pattern of apatite (in Shergotty) is light REE-enriched. Parent magmas are calculated from the modal compositions of residues of ALHA 77005, Shergotty, and EETA 79001. The parent magmas lack a Eu anomaly, indicating that plagioclase was a late-stage crystallizing phase and that it probably crystallized before the phosphates. The parent magmas of ALHA 77005 and Shergotty have similar REE patterns, with a subchondritic Nd/Sm ratio. However, the Sm/Nd isotopoics require a light REE-depleted source for ALHA 77005 (if the crystallization age is less than 600 Myr) and a light REE-enriched source for Shergotty. Distant Nd and Sr isotopic signatures may suggest different source regions for shergottites.

Laul, J. C.↗

NASA NTRS1987

A new VLSI complex integer multiplier which uses a quadratic-polynomial residue system with Fermat numbers

Shyu, H. C.↗

NASA NTRS1987

The global residual mean circulation in the middle atmosphere for the northern winter period

The residual mean circulation (rmc) has been calculated from the transformed thermodynamic equation using LIMS (Limb Infrared Monitor of the Stratosphere) data for the 100-0.1 mb region. For discussion, it has been divided into two components: the diabatic circulation, associated with the diabatic heating, and the transient circulation, more directly connected to eddy activity. The slowly varying diabatic circulation reveals an equator-to-pole circulation at lower levels in the stratosphere, usually overlain by a summer-to-winter pole circulation. However, there are strong seasonal variations, so that the pole-to-pole circulation fills the entire region at the December solstice, while the equator-to-pole circulation extends to above 0.1 mb at the equinoxes. The transient circulation is characterized by rapid variations and small vertical and horizontal scales. Though generally smaller than the diabatic circulation, it can dominate in the lower stratosphere during disturbed conditions. This circulation is consistent with the transformed momentum equation in the lower stratosphere (where drag is expected to be small) during undisturbed periods. It suggests a large drag due to small-scale waves (such as gravity waves) in the mesosphere, although the magnitudes are uncertain. The downward propagation of the semiannual oscillation causes the rmc in the tropics to vary, and it is capable of creating the equatorial water vapor maximum above 10 mb.

Gille, John C.↗

NASA NTRS1987

Microstructure-derived macroscopic residual resistance of brominated graphite fibers

The microscopic bromine distribution in pitch-based brominated graphite fibers has been measured with a scanning transmission electron microscope by monitoring the Br K alpha1 X-ray intensity. An imhomogeneous distribution of Br along the fiber is found with two distinct cross-sectional distributions, namely, a uniform distribution in Br-rich regions and a Gaussian-like distribution in Br-poor regions. A model based on these Br distribution measurements is proposed to understand the relation between the Br microstructure and the macroscopic residual resistance of the fiber. This model yields semiquantitative agreement with experimental results.

Qian, X. W.↗

NASA NTRS1987

Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. I - Theoretical considerations

The hole-drilling technique for the measurement of residual stresses using electrical resistance strain gages has been widely used for isotropic materials and has been adopted by the ASTM as a standard method. For thin isotropic plates, with a hole drilled through the thickness, the idealized hole-drilling calibration constants are obtained by making use of the well-known Kirsch's solution. In this paper, an analogous attempt is made to theoretically determine the three idealized hole-drilling calibration constants for thin orthotropic materials by employing Savin's (1961) complex stress function approach.

Prasad, C. B.↗

NASA NTRS1987

Implementation of a fast digital optical matrix-vector multiplier using a holographic look-up table and residue arithmetic

The design and implementation of a digital (numerical) optical matrix-vector multiplier are presented. A Hughes liquid crystal light valve, the residue arithmetic representation, and a holographic optical memory are used to construct position coded optical look-up tables. All operations are performed in effectively one light valve response time with a potential for a high information density.

Habiby, Sarry F.↗

NASA NTRS1987

Determination of calibration constants for the hole-drilling residual stress measurement technique applied to orthotropic composites. II - Experimental evaluations

The first step in the extension of the semidestructive hole-drilling technique for residual stress measurement to orthotropic composite materials is the determination of the three calibration constants. Attention is presently given to an experimental determination of these calibration constants for a highly orthotropic, unidirectionally-reinforced graphite fiber-reinforced polyimide composite. A comparison of the measured values with theoretically obtained ones shows agreement to be good, in view of the many possible sources of experimental variation.

Prasad, C. B.↗

NASA NTRS1987

Non-enzymatic transcription of an oligodeoxynucleotide 14 residues long

Nonenzymatic synthesis of oligodeoxynucleotides up to 14 residues long from 2-MeImpG and 2-MeImpC mononucleotides was demonstrated. The synthesis is primed by 14-mer and 15-mer oligonucleotides d(C3GC3GC3GC2) and d(C3GC3GC3GC3) as templates. The predominant products are a series of 3-prime-5-prime-linked oligonucleotides, complementary to the template, ranging in length from GGC to GGCGGGCGGGCGGG. The 15-mer template directed the synthesis of the same family of products that were formed on the 14-mer template. This finding is explained by the preferential conversion of the dimer GG to GGC rather than to GGG. In the context of molecular evolution, these results suggest that the detailed kinetics of template-directed synthesis could form the basis for the selection of one replicating oligonucleotide from a family of closely related oligonucleotides.

Acevedo, Oscar L.↗