Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Examination”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Examination of coating failure by acoustic emission

Coatings of NiCrAlY bond coat with a zirconia - 12 wt percent yttria overlay were applied to disc-shaped specimens of U-700 alloy. A waveguide of 1 mm diameter platinum was TIG welded to the specimen and allowed it to be suspended in a tubular furnace. The specimen was thermally cycled to 1150 C, and the acoustic emission (AE) monitored. The weight gain per thermal cycle was also measured. A computer system based on the IBM-XT microcomputer was used extensively to acquire the AE data with respect to temperature. This system also controlled the temperature by using a PD software loop. Several different types of AE analyses were performed. A major feature of these tests, not addressed by previous work in this area, was that the coatings covered 100 percent of the specimen and also that the AE was amplified at two different levels. It is believed that this latter feature allows a qualitative appraisal of the relative number of cracks per AE event. The difference in AE counts between the two channels is proportional to the number of cracks per AE event, and this parameter may be thought of as the crack density. The ratio of the AE count difference to the AE count magnitude of one channel is inversely proportional to the crack growth. Both of these parameters allow the crack distribution and crack growth within each specimen to be qualitatively followed during the thermal cycling operation. Recent results which used these principles will be presented.

Berndt, Christopher C.↗
NASA NTRS1989

Plume characteristics of MPD thrusters: A preliminary examination

A diagnostics facility for MPD thruster plume measurements was built and is currently undergoing testing. The facility includes electrostatic probes for electron temperature and density measurements, Hall probes for magnetic field and current distribution mapping, and an imaging system to establish the global distribution of plasma species. Preliminary results for MPD thrusters operated at power levels between 30 and 60 kW with solenoidal applied magnetic fields show that the electron density decreases exponentially from 1x10(2) to 2x10(18)/cu m over the first 30 cm of the expansion, while the electron temperature distribution is relatively uniform, decreasing from approximately 2.5 eV to 1.5 eV over the same distance. The radiant intensity of the ArII 4879 A line emission also decays exponentially. Current distribution measurements indicate that a significant fraction of the discharge current is blown into the plume region, and that its distribution depends on the magnitudes of both the discharge current and the applied magnetic field.

Myers, Roger M.↗
NASA NTRS1989

Morphological transitions in the rapid solidification regime - A re-examination of the fundamental validity of the absolute stability concept of Mullins and Sekerka

The validity of the notion of absolute stability (AS) of a planar solid-liquid interface, proposed by Mullins and Sekerka (M-S, 1964), was tested using experimental data obtained for a number of dilute Ag-Cu and Sn-In alloys and for ultrahigh-purity succinonitrile. It is shown that the restriction applied by the M-S theory is satisfied during the steady-state planar solidification in an undercooled melt, provided the undercooling is quite small. The findings obtained on the Ag-Cu and Sn-In alloys are compared with early measurements by Davis and Fryzuk (1971) in dilute Sn-In alloys with 25 to 400 ppm additions of In.

Laxmanan, V.↗
NASA NTRS1989

Use of an expansion tube to examine scramjet combustion at hypersonic velocities

Combustion testing at total enthalpy conditions corresponding to flight Mach numbers in excess of 12 requires the use of impulse facilities. The expansion tube is the only operational facility of its size which can provide these conditions without excessive oxygen dissociation or driver gas contamination. Expansion tube operation is described herein and the operational parameters having the largest impact on its performance are determined. These are: driver-to-intermediate chamber pressure ratio, driver gas molecular weight and specific heat ratio, and driver gas temperature. Increases in the last-named parameter will markedly affect the test section static pressure. Preliminary calibration tests are discussed and test gas conditions which have been achieved are presented. Calculated and experimental test times are compared and the parameters affecting test time are discussed. The direction of future work using this important experimental tool is indicated.

Rizkalla, O.↗
NASA NTRS1989

Plume characteristics of MPD thrusters - A preliminary examination

A diagnostics facility for MPD thruster plume measurements has been built and is currently undergoing testing. The facility includes electrostatic probes for electron temperature and density measurements, Hall probes for magnetic field and current distribution mapping, and an imaging system to establish the global distribution of plasma species. Preliminary results for MPD thrusters operated at power levels between 30 and 60 kW with solenoidal applied magnetic fields show that the electron density decreases exponentially from 1 x 10 to the 20th/cu m to 2 x 10 to the 18th/cu m over the first 30 cm of the expansion, while the electron temperature distribution is relatively uniform, decreasing from approximately 2.5 eV to 1.5 eV over the same distance. The radiant intensity of the ArII 4879 A line emission follows similar patterns. Current distribution measurements indicate that significant fraction of the discharge current is blown into the plume region, and that its distribution depends on the magnitudes of both the discharge current and the applied magnetic field.

Myers, R. M.↗
NASA NTRS1990

Experiment K-6-13. Morphological and biochemical examination of heart tissue. Part 1: Effects of microgravity on the myocardial fine structure of rats flown on Cosmos 1887. Ultrastructure studies. Part 2: Cellular distribution of cyclic ampdependent protein kinase regulatory subunits in heart muscle of rats flown on Cosmos 1887

The left ventricle of hearts from rats flown on the Cosmos 1887 biosatellite for 12.5 days was compared to the same tissue of synchronous and vivarium control animals maintained in a ground based laboratory. The volume density of the mitochondria in the myocardium of the space-flown animals was statistically less (p equal less than 0.01) than that of the synchronous or vivarium control rats. Exposure to microgravity resulted in a certain degree of myocardial degeneration manifested in mitochondrial changes and accumulation of myeloid bodies. Generalized myofibrillar edema was also observed.

Philpott, D. E.↗
NASA NTRS1990

Experiment K-6-16. Morphological examination of rat testes. The effect of Cosmos 1887 flight on spermatogonial population and testosterone level in rat testes

Testes from rats flown on Cosmos 1887 for twelve and a half days were compared to basal control, synchronous control and vivarium maintained rats. When the mean weights of flight testes, normalized for weight/100 gms, were compared to the vivarium controls they were 6.7 percent lighter. Although the flight testes were lighter than the synchronous, the difference is not significant. Counts of spermatogonial cells from 5 animals in each group revealed a 4 percent decrease in flight compared to vivarium controls. In both cases the t-Test significance was less than 0.02. The serum testosterone levels of all animals (flight, synchronous and vivarium) were significantly below the basal controls.

Philpott, D. E.↗
NASA NTRS1988

An examination of automation and robotics in the context of Space Station operations

A NASA-sponsored review of Space Station automation and robotics (A&R) applications from an operations and utilization perspective is presented. The goals of the A&R panel and this report are to identify major suggestions for advanced A&R operations application in Space Station as well as key technologies that have emerged or gained prominence since the completion of previous reports; to review and incorporate the range of possible Space Station A&R applications into a framework for evaluation of A&R opportunities; and to propose incentives for the government, work packages, and subcontractors to more aggressively identify, evaluate, and incorporate advanced A&R in Space Station Operations. The suggestions for A&R focused on narrow objectives using a conservative approach tuned to Space Station at IOC and limiting the Station's growth capabilities. A more aggressive stance is to identify functional needs over the Program's life, exploit and leverage available technology, and develop the key advanced technologies permitting effective use of A&R. The challenge is to systematically identify candidate functions to be automated, provide ways to create solutions resulting in savings or increased capabilities, and offer incentives that will promote the automation.

Criswell, David R.↗
NASA NTRS1989

A re-examination of impulsive VLF signals in the night ionosphere of Venus

Consideration is given to the impulsive electrical signals clustered around periapsis which were observed by the Pioneer Venus Orbiter Electric Field Detector. The study of these signals by Singh and Russell is repeated, taking into account the telemetry errors noted by Taylor and Cloutier (1988). It is found that there is naturally occurring noise in the dark ionosphere of Venus near periapsis. The absolute rates of occurrence are determined, showing differences with the results from the original study.

Russell, C. T.↗
NASA NTRS1990

Shock waves in mixtures - A re-examination

The structure of normal shock waves in binary mixtures is analyzed, using Monte Carlo direct simulation, and compared with previous experimental data. Previous work by Erwin et al. used a collision method based directly on the intermolecular potential function; the present work extends this approach to binary mixtures, obtaining heteromolecular collision cross sections from the corresponding potentials. Results are presented for helium-argon mixtures, with conditions corresponding to the experiments of Harnett and Muntz (1972).

Erwin, Daniel A.↗
NASA NTRS1990

Preliminary crystallographic examination of a novel fungal lysozyme from Chalaropsis

The lysozyme from the fungus of the Chalaropsis species has been crystallized. This lysozyme displays no sequence homology with avian, phage, or mammalian lysozymes, however, preliminary studies indicate significant sequence homology with the bacterial lysozyme from Streptomyces. Both enzymes are unusual in possessing beta-1,4-N-acetylmuramidase and beta-1,4-N,6-O-diacetylmuramidase activity. The crystals grow from solutions of ammonium sulfate during growth periods from several months to a year. The space group is P2(1)2(1)2(1) with a = 34.0 A, b = 42.6 A, c = 122.1 A. Preliminary data indicate that there is 1 molecule/asymmetric unit.

Carter, Daniel C.↗
NASA NTRS1991

Results of examination of silvered Teflon from the Long Duration Exposure Facility

Pieces of silvered Teflon thermal control blanket from seventeen locations on the Long Duration Exposure Facility (LDEF) were studied. Results of the measurements of surface texturing, and mechanical, electrical and thermal properties are presented. Photos of the blankets, scanning electron microscope pictures, infrared spectra, and surface analysis results are presented. Contamination issues relative to performance of the blankets are discussed. The variation in measured properties are reported as a function of exposure conditions.

Rousslang, Ken W.↗
NASA NTRS1991

Passive exposure of Earth radiation budget experiment components LDEF experiment AO-147: Post-flight examinations and tests

The Passive Exposure of Earth Radiation Budget Experiment Components (PEERBEC) experiment of the Long Duration Exposure Facility (LDEF) mission was composed of sensors and components associated with the measurement of the earth radiation budget (ERB) from satellites. These components included the flight spare sensors from the ERB experiment which operated on Nimbus 6 and 7 satellites. The experiment components and materials as well as the pertinent background and ancillary information necessary for the understanding of the intended mission and the results are described. The extent and timing of the LDEF mission brought the exposure from solar minimum between cycles 21 and 22 through the solar maximum of cycle 22. The orbital decay, coupled with the events of solar maximum, caused the LDEF to be exposed to a broader range of space environmental effects than were anticipated. The mission spanned almost six years concurrent with the 12 year (to date) Nimbus 7 operations. Preliminary information is presented on the following: (1) the changes in transmittance experienced by the interference filters; (2) the results of retesting of the thermopile sensors, which appear to be relatively unaffected by the exposure; and (3) the results of the recalibration of the APEX cavity radiometer. The degradation and recovery of the filters of the Nimbus 7 ERB are also discussed relative to the apparent atomic oxygen cleaning which also applies to the LDEF.

Hickey, John R.↗
NASA NTRS1991

An examination of coherent structures in a lobed mixer using multifractal measures in conjunction with the proper orthogonal decomposition

A 'lobed mixer' device that enhances mixing through secondary flows and streamwise vorticity is presently studied within the framework of multifractal-measures theory, in order to deepen understanding of velocity time trace data gathered on its operation. Proper orthogonal decomposition-based knowledge of coherent structures has been applied to obtain the generalized fractal dimensions and multifractal spectrum of several proper eigenmodes for data samples of the velocity time traces; this constitutes a marked departure from previous multifractal theory applications to self-similar cascades. In certain cases, a single dimension may suffice to capture the entire spectrum of scaling exponents for the velocity time trace.

Ukeiley, L.↗
NASA NTRS1991

Comment on 'A re-examination of impulsive VLF signals in the night ionosphere of Venus'

Taylor and Cloutier (TC, 1988) previously argued that Singh and Russell (SR, 1986) wrongly identified telemetry interference as VLF broadband signals originating in Venus 'lightning events'. A response was made by Russell and Singh (RS, 1989). This comment criticizes RS, arguing that the SR did not distinguish between signal and noise and that RS makes false claims about the SR analysis. In a reply to TC, Russell argues that the SR paper, while flawed, was not intended to be quantitative and succeeds in bringing attention to the morphology of the signals seen in the upper three channels of the Pioneer Venus electric field detector.

Taylor, H. A., Jr.↗
NASA NTRS1990

Examination of the use of narrowband radiances for earth radiation budget studies

The relationship between narrowband and broadband thermal radiances is explored to determine the accuracy of outgoing longwave radiation derived from narrowband data. Infrared window (11.5 microns) data from the Geostationary Operational Environmental Satellite are correlated with longwave (5.0 - 50.0 microns) data from the Earth Radiation Budget Experiment. A simple quadratic fit between the narrowband and longwave fluxes results in a standard error of the estimate of 4.5-5.3 percent for data which are matched closely in time and space. Use of matched regional flux data with temporal differences up to a half hour yield standard errors of 4.6-5.9 percent. About one fourth of the magnitude of the error may be attributed to limb-darkening and temporal differences in the matched fluxes. The relationship shows a significant dependence on the relative humidity of the atmosphere above the radiating surface. Although this dependency accounts for only about 2 percent of the standard error, it reduces the monthly mean regional errors by more than 10 percent. Data taken over land produced a slightly different relationship than data taken over water. The differences appear to be due to the higher altitudes of the land radiating surfaces. Cloud amount and height also influence the narrowband-broadband relationship. Inclusion of these parameters does not affect the standard errors but it reduces the montly mean regional errors by another 10 percent. Better humidity and temperature data and knowledge of cloud microphysics may be required to further improve the relationship. Using the best fits, it is concluded that the monthly mean outgoing flux may be determined with an rms uncertainty of 1.7 percent using a single infrared window channel with coincident cloud and humidity data. Regional concentrations of the errors, however, make the use of narrowband data too unreliable for monitoring the longwave flux for climate change studies.

Young, David F.↗
NASA NTRS1989

Preliminary examination of the Yamato-86032 lunar meteorite. II - Major and trace element chemistry

Results of the chemical composition analysis of Yamato-86032, found in Antarctica in 1986, are summarized. The meteorite may be classified as an anorthositic breccia, but its trace element composition is different from the composition of the other known lunar meteorites. The major element chemistry of Y-86032 is similar to the other lunar meteorites, except for the iron content, which is lower by a factor of about 1.4. The abundances of incompatible and lithophile elements such as Zr, Hf, Ta, Th, or the REEs are very low and comparable to Y-82192/3. Other elements, in particular Fe, Ti, Sc, Cr, Mn, and Co, have lower abundances in Y-86032 than in Y-82192/3. Variations between individual analysis demonstrate that the rock itself is heterogeneous.

Koeberl, Christian↗