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NASA NTRS1982

Equivalent damage: A critical assessment

Concepts in equivalent damage were evaluated to determine their applicability to the life prediction of hot path components of aircraft gas turbine engines. Equivalent damage was defined as being those effects which influence the crack initiation life-time beyond the damage that is measured in uniaxial, fully-reversed sinusoidal and isothermal experiments at low homologous temperatures. Three areas of equivalent damage were examined: mean stress, cumulative damage, and multiaxiality. For each area, a literature survey was conducted to aid in selecting the most appropriate theories. Where possible, data correlations were also used in the evaluation process. A set of criteria was developed for ranking the theories in each equivalent damage regime. These criteria considered aspects of engine utilization as well as the theoretical basis and correlative ability of each theory. In addition, consideration was given to the complex nature of the loading cycle at fatigue critical locations of hot path components; this loading includes non-proportional multiaxial stressing, combined temperature and strain fluctuations, and general creep-fatigue interactions. Through applications of selected equivalent damage theories to some suitable data sets it was found that there is insufficient data to allow specific recommendations of preferred theories for general applications. A series of experiments and areas of further investigations were identified.

Laflen, J. R.↗

NASA NTRS1982

Methodology of remote sensing data interpretation and geological applications

Elements of photointerpretation discussed include the analysis of photographic texture and structure as well as film tonality. The method used is based on conventional techniques developed for interpreting aerial black and white photographs. By defining the properties which characterize the form and individuality of dual images, homologous zones can be identified. Guy's logic method (1966) was adapted and used on functions of resolution, scale, and spectral characteristics of remotely sensed products. Applications of LANDSAT imagery are discussed for regional geological mapping, mineral exploration, hydrogeology, and geotechnical engineering in Brazil.

Parada, N. D. J.↗

NASA NTRS1983

Requirements of constitutive models for two nickel-base superalloys

The constitutive behavior of two nickel-base superalloys, Rene '80 and Inconel 718, utilized in gas turbine blade and disk components, respectively, is presented. In turbine blade applications, the high homologous temperatures result in strain-rate effects dominating behavior. In turbine disks, the temperatures are cooler so that mean stress effects become important. The impact of these two variables on the overall crack initiation lifetime and analysis methodology is discussed.

Laflen, J. H.↗

NASA NTRS1983

Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8at.% Al

A study of the elevated temperature slow plastic flow properties of the B2 aluminide Fe-39.8at.% Al was undertaken. Polycrystalline materials possessing several different microstructures were produced by the hot extrusion of prealloyed powder and, in some cases, postextrusion heat treatments. Compression tests were conducted in air at 1200, 1300 and 1400 K. Such testing revealed that the extrusion temperature affected the active deformation mechanisms where material extruded at 1505 K had a stress exponent about twice that of the intermetallic extruded at 1200 K. Grain size refinement to about 10 microns was found to strengthen the Fe-39.8at.% Al material; unfortunately, the effectiveness of such strengthening is limited to a homologous temperature of about 0.75 for strain rates of commercial interest (less than 10 to the -7th/sec).

Whittenberger, J. D.↗

NASA NTRS1983

The 1981 July 26-27 flares - Magnetic developments leading to and following flares

The present investigation is concerned with an approach which makes it possible to determine the key factors in flare production on the basis of a broad range of observations. The considered observations are related to a study of at least 10 flares in Hale region 17760 between 17:00 UT 1981 July 26 and 18:00 UT 1981 July 27. Attention is given to the optical data and phenomenology of the flares. On the basis of the presented data, it is concluded that flares recurred in a number of areas in the region, each of which was marked by flux emergence. In each area, flaring ceased after flux emergence and spot motion ceased. Flares occur at points where the magnetic field is stressed by changes associated with sunspot evolution, normally flux emergence. Homologous flares in H-alpha reflect the general magnetic layout of the local area in which they occur.

Zirin, H.↗

NASA NTRS1984

Energy balance of stellar coronae. III - Effect of stellar mass and radius

A homologous transformation is derived which permits the application of the numerical coronal models of Hammer from a star with solar mass and radius to other stars. This scaling requires a few approximations concerning the lower boundary conditions and the temperature dependence of the conductivity and emissivity. These approximations are discussed and found to be surprisingly mild. Therefore, the scaling of the coronal models to other stars is rather accurate; it is found to be particularly accurate for main-sequence stars. The transformation is used to derive an equation that gives the maximum temperature of open coronal regions as a function of stellar mass and radius, the coronal heating flux, and the characteristic damping length over which the corona is heated.

Hammer, R.↗

NASA NTRS1985

The Scaling of Coronal Models from One Star to Another

The requirements that must be met in order that stationary numerical corona models can be scaled from one star to another are discussed. A corona model is a solution of the conservation equations for mass, momentum, and energy, subject to appropriate boundary conditions, and of the equation of state. In general, the mass M and radius R of the star enter these equations and boundary conditions as free parameters. A given solution can be scaled to other stars only if all equations can be rewritten in such a form that M and R do no longer appear explicitly as free parameters, but only implicitly as scaling factors of the variables. An adequate means to find these scaling factors is a homologous transformation: one multiplies all variables and parameters by separate constants (i.e., scaling factors) and requires that the equations and boundary conditions remain valid. This leads to a set of nonlinear relations between the transformation constants. Only if in this set the two constants associated with M and R can be chosen independently, can a given numerical corona model be scaled to arbitrary stars.

Hammer, R.↗

NASA NTRS1984

Moon

The present state and evolution of the physical features which are visible on the Moon's surface are emphasized herein. Lunar craters, their distribution and stratigraphy, and the cratering processes are addressed. Homologous material is presented for lunar basins. Terra breccias, maria, and mare basalts are discussed. Lunar geologic history is also considered.

Don E Wilhelms↗

NASA NTRS1985

Is fast fiber innervation responsible for increased acetylcholinesterase activity in reinnervating soleus muscles?

An investigation was conducted as to whether the predominantly slow SOL, which is low in AChE activity, is initially reinnervated by axons that originally innervated fast muscle fibers with high AChE activity, such as those of the EDL. Local denervation of the SOL in the guinea pig was performed because this muscle is composed solely of slow (type I) fibers; thereby virtually eliminating the possibility of homologous muscle fast fiber innervation. The overshoot in this preparation was qualitatively similar to that seen with distal denervation in the guinea pig and local and distal denervation in the rat. Thus, initial fast fiber innvervation is not responsible for the patterns of change in AChE activity seen with reinnervation in the SOL. It is concluded that the neural control of AChe is different in these two muscles and may reflect specific differences in the characteristics of AChE regulation in fast and slow muscle.

Misulis, K. E.↗

NASA NTRS1984

Recurrent mass ejections observed in H-alpha and CIV

Time sequences of recurrent mass ejections have been observed during a coordinated SMY program (Sept. 1, 1980 - Sept. 23, 1980 - Oct. 2, 1980). Comparison of the temporal evolution of H-alpha and CIV brightnesses shows a weak phase lag between H-alpha and CIV maxima, in the case of homologous flares, with CIV brightness maxima preceding H-alpha maxima. The analysis of the variation of the ejection velocities is expected to lead to the determination of an energy balance. Such recurrent ejections could be due to periodic energy storage and periodic reorganization of magnetic field as envisaged to occur for flares, but at lower energy levels.

Schmieder, B.↗

NASA NTRS1985

Results from observations of the 15 June 1983 occultation by the Neptune system

Observations of eight Neptune occultations from six sites in the southwestern Pacific on June 15, 1983. The data were used to search for evidence of rings around Neptune down to a distance of 0.03 Neptune radii from the planetary surface, but the results were negative. An astrometric analysis of the timings yielded solution for the equatorial radius a(0) of Neptune at 1 microbar pressure and the oblatness e at this level. The results are: a(0) = 25,295 + or - 50 km; e = 0.022 + or - 0.004, from which a value for a(1) (equatorial radius at 1 bar pressure) of 24,830 + or - 100 km; and a rotation period of P = 15 h (+3, -2 h) is derived. These results are based on a recent determination of Neptune's pole position and mass quadruple moment, and are consistent with the hypothesis that Neptune and Uranus have homologous mass distributions, although the constraint on interior structure is a weak one. If the probable uncertainty of the pole position is taken into account, error bars on e and derived quantities should be increased by about 50 percent. The present determinations of Neptune atmospheric temperatures at 1 microbar are consistent with earlier results and when combined with all previous data give an average value of 156 + or - 10 K. There is only slight evidence for any latitude dependence in the temperatures. Profiles with a high signal-to-noise ratio suggest the possible presence of an absorbing layer at altitudes higher than the 1-microbar level.

Hubbard, W. B.↗

NASA NTRS1985

What are mycoplasmas - The relationship of tempo and mode in bacterial evolution

In phenotype the mycoplasmas are very different from ordinary bacteria. However, genotypically (i.e., phylogenetically) they are not. On the basis of ribosomal RNA homologies the mycoplasmas belong with the clostridia, and indeed have specific clostridial relatives. Mycoplasmas are, however, unlike almost all other bacteria in the evolutionary characteristics of their ribosomal RNAs. These RNAs contain relatively few of the highly conserved oligonucleotide sequences characteristic of normal eubacterial ribosomal RNAs. This is interpreted to be a reflection of an elevated mutation rate in mycoplasma lines of descent. A general consequence of this would be that the variation associated with a mycoplasma population is augmented both in number and kind, which in turn would lead to an unusual evolutionary course, one unique in all respects. Mycoplasmas, then, are actually tachytelic bacteria. The unusual evolutionary characteristics of their ribosomal RNAs are the imprints of their rapid evolution.

Woese, C. R.↗

NASA NTRS1985

Direct coupling of microbore HPLC columns to MS systems

A detailed investigation using electron microscopy was conducted which examined the conditions of materials used in the construction of stable, high performance microbore liquid chromatography (LC) columns. Small details proved to be important. The effects of temperature on the elution of several homologous series used as probe compounds was examined in reverse phase systems. They showed that accessible temperature changes provide roughly half the increase in solvent strength that would be obtained going from a 100% aqueous to a 100% organic mobile phase, which is sufficient to warrant their use in many analyses requiring the use of gradients. Air circulation temperature control systems provide the easiest means of obtaining rapid, wide range changes in column temperature. However, slow heat transfer from the gas leads to thermal nonuniformity in the column and a decrease in resolution as the temperature program progresses.

Mcnair, H. M.↗

NASA NTRS1986

Functional and evolutionary relationships between bacteriorhodopsin and halorhodopsin in the archaebacterium, halobacterium halobium

The archaebacteria occupy a unique place in phylogenetic trees constructed from analyses of sequences from key informational macromolecules, and their study continues to yield interesting ideas on the early evolution and divergence of biological forms. It is now known that the halobacteria among these species contain various retinal-proteins, resembling eukaryotic rhodopsins, but with different functions. Two of these pigments, located in the cytoplasmic membranes of the bacteria, are bacteriorhodopsin (a light-driven proton pump) and halorhodopsin (a light-driven chloride pump). Comparison of these systems is expected to reveal structure/function relationships in these simple (primitive?) energy transducing membrane components and evolutionary relationships which had produced the structural features which allow the divergent functions. Findings indicate that very different primary structures are needed for these proteins to accomplish their different functions. Indeed, analysis of partial amino acid sequences from halo-opsin shows already that few if any long segments exist which are homologous to bacterio-opsin. Either these proteins diverged a very long time ago to allow for the observed differences, or the evolutionary clock in the halobacteria runs faster than usual.

Lanyi, J. K.↗

NASA NTRS1986

A method for developing design diagrams for ceramic and glass materials using fatigue data

The service lifetime of glass and ceramic materials can be expressed as a plot of time-to-failure versus applied stress whose plot is parametric in percent probability of failure. This type of plot is called a design diagram. Confidence interval estimates for such plots depend on the type of test that is used to generate the data, on assumptions made concerning the statistical distribution of the test results, and on the type of analysis used. This report outlines the development of design diagrams for glass and ceramic materials in engineering terms using static or dynamic fatigue tests, assuming either no particular statistical distribution of test results or a Weibull distribution and using either median value or homologous ratio analysis of the test results.

Heslin, T. M.↗

NASA NTRS1985

New perspectives on bacterial ferredoxin evolution

Ferredoxins are low-molecular-weight, nonheme, iron proteins which function as electron carriers in a wide variety of electron transport chains. Howard et al. (1983) have suggested that the amino end of Azotobacter vinelandii ferredoxin shows a greater similarity to the carboxyl end of ferredoxin from Chromatium vinosum and that their half-chain sequences are homologous when the half-chains of either species are considered in inverse order. Examination of this proposition has made it necessary to reevaluate previous conclusions concerning the evolution of bacterial ferredoxin. Attention is given to the properties of the bacterial ferredoxin sequences, and the evolution of the bacterial ferredoxins.

George, D. G.↗

NASA NTRS1985

Phylogenetic origins of the plant mitochondrion based on a comparative analysis of 5S ribosomal RNA sequences

The complete nucleotide sequences of 5S ribosomal RNAs from Rhodocyclus gelatinosa, Rhodobacter sphaeroides, and Pseudomonas cepacia were determined. Comparisons of these 5S RNA sequences show that rather than being phylogenetically related to one another, the two photosynthetic bacterial 5S RNAs share more sequence and signature homology with the RNAs of two nonphotosynthetic strains. Rhodobacter sphaeroides is specifically related to Paracoccus denitrificans and Rc. gelatinosa is related to Ps. cepacia. These results support earlier 16S ribosomal RNA studies and add two important groups to the 5S RNA data base. Unique 5S RNA structural features previously found in P. denitrificans are present also in the 5S RNA of Rb. sphaeroides; these provide the basis for subdivisional signatures. The immediate consequence of obtaining these new sequences is that it is possible to clarify the phylogenetic origins of the plant mitochondrion. In particular, a close phylogenetic relationship is found between the plant mitochondria and members of the alpha subdivision of the purple photosynthetic bacteria, namely, Rb. sphaeroides, P. denitrificans, and Rhodospirillum rubrum.

Villanueva, E.↗

NASA NTRS1985

Amino acids of the Murchison meteorite. II - Five carbon acyclic primary beta-, gamma-, and delta-amino alkanoic acids

The five-carbon acyclic primary beta, gamma, and delta amino alkanoic acids of the Murchison meteorite are studied using gas chromatography-mass spectrometry and ion exchange chromatography. The chromatograms reveal that alpha is the most abundant monoamino alkanoic acid followed by gamma and beta, and an exponential increase in the amount of amino acid is observed as the carbon number increases in the homologous series. The influence of frictional heating, spontaneous thermal decomposition, and radiation of the synthesis of amino acids is examined. The data obtained support an amino acid synthesis process involving random combination of single-carbon precursors.

Cronin, J. R.↗