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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Hybrid Physics-Based, Data-Driven Approach to Model Damage Accumulation in Corrosion of Polymeric Adhesives

The degradation of polymeric adhesives in dissimilar joints is a menace to electric and structural components of the automotive industry. In polymeric adhesives, failure often occurs due to damage accumulated from discrete environmental sources—thermal degradation, oxidation, hydrolysis, radiation, and moisture—that are combined with progressive damage mechanisms, such as aging and fatigue. Because most damage mechanisms that lead to degradation act in parallel, the estimation of the lifetime of a polymeric material becomes a significant reliability issue, no study currently exists that can simultaneously consider even two of these phenomena. Most current efforts are directed toward a single-phenomenon, single-model approach in which a model is developed to cover one specific damage mechanism. While this approach is advantageous in exploring single mechanisms, it is strongly inconclusive for degradation that occurs by multiple damage mechanisms. Our team plans to take a fresh perspective by designing a hybrid constitutive/data-driven approach that allows models of different damage mechanisms to be integrated into one model and then used to explore the degradation-induced failure of polymeric adhesives. The theoretical-computational part of this work is divided into four research components as described in the Approach section below.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Attitude-referenced radiometer study. Part 2: Primary calibration system

A primary calibration system, PCS, for infrared radiometers has been developed, built, and tested. The system allows radiometers to be calibrated with less than 1 percent error for use in earth coverage horizon measurements, earth resources surveys, and synoptic meteorological measurement. The final design, fabrication and test of the PCS are reported. A detailed description of the PCS construction is presented, along with the results of a complete series of functional tests. Test to verify the source thermal characteristics, collimator reflectance, and output beam characteristics are described and their results presented.

Williamson, W. R.↗
NASA NTRS1972

Simulation of superposed coherent and chaotic radiation of arbitrary spectral shape.

A simulation technique is described and utilized to generate superposed coherent and chaotic (thermal) radiation of arbitrary spectral shape. The statistical properties of a simulated radiation field with a Lorentzian spectral density are investigated with a photoelectron counting experiment. The experimental photocount distribution and normalized mth-order factorial moments are compared to theory and verify that the simulated radiation field, an appropriately modulated laser beam, has the expected statistical properties. The concept described indicates that one may, in principle, generate a thermal source of comparable intensity to that of a laser, arbitrary spectral shape, and bandwidth.

Ruggieri, N. F.↗
NASA NTRS1973

Composition and physics of the lunar atmosphere.

The existence in the lunar atmosphere of helium, neon, argon, and possibly molecular hydrogen has been confirmed by the Apollo 17 mass spectrometer. The observed helium concentrations and distribution agree closely with model predictions for a non-condensable gas based on a solar wind source, thermal escape and a Monte Carlo random walk calculated longitudinal distribution. Heavier gases are lost by photoionization and subsequent sweeping away by the solar wind electric field. The observed nighttime neon concentration of 80,000 molecules per cu cm is consistent with expected amounts. Argon, however, is adsorbed on the lunar surface late at night when the surface temperature is lowest. It shows the expected predawn enhancement exhibited by condensable gases released into the atmosphere at the sunrise terminator. Hydrogen appears to exist in the molecular rather than atomic state. Its observed concentration is less than a factor of 3 higher than that predicted by a model similar to that used for helium.

Hoffman, J. H.↗
NASA NTRS1977

SETI - A preliminary search for narrowband signals at microwave frequencies

In the search for intelligent signals of extraterrestrial origin, certain forms of signals merit immediate and special attention. Extremely narrowband signals of spectral width similar to our own television transmissions are most favored energetically and least likely to be confused with natural celestial emission. A search of selected stars has been initiated using observational and data processing techniques optimized for the detection of such signals. These techniques allow simultaneous observation of 10 to the 5th to 10 to the 6th channels within the observed spectral range. About two hundred nearby (within 80 LY) solar type stars have been observed at frequencies near the main microwave transitions of the hydroxyl radical. In addition, several molecular (hydroxyl) masers and other non-thermal sources have been observed in this way in order to uncover any possible fine spectral structure of natural origin and to investigate the potential of such an instrument for radioastronomy.

Cuzzi, J. N.↗
NASA NTRS1979

A solid-state phase-insensitive ultrasonic transducer

Photoconductive acoustoelectric transducer (AET) functions as phase-insensitive ultrasonic transducer. Device is easy to use and requires no additional noisy components such as light or thermal source.

Heyman, J. S.↗
NASA NTRS1978

Observations of the hard X-ray spectrum of the impulsive phase of solar flares

The impulsive solar hard X-ray spectrum provides a direct diagnostic on the impulsive energy release of the flare. The data from the hard X-ray (14-342 keV) spectrometer on OSO 7 have been examined for events covering a wide energy range to determine the photon spectrum more precisely. This resulted in a sample of 38 events. The data have been fitted with either single- or double-power laws, and with an exponential spectrum, as from thermal bremsstrahlung. The chi-squared statistic between two-parameter fits strongly favors the exponential fit, particularly at peak intensity when the widest energy range is sampled. This result supports a single-temperature thermal source of the impulsive solar hard X-rays with temperatures in the range 4.7-31 keV and emission measures in the range from 8.4 x 10 to the 43rd to 6.0 x 10 to the 46th per cu cm. The temperature reaches a single maximum and then rapidly decays, but the emission measure usually increases throughout, even after temperature maximum, for data with 10-s resolution.

Elcan, M. J.↗
NASA NTRS1981

Continental rifting - Progress and outlook

It is noted that in spite of the flood of new data on continental rifts in the last 15 years, there is little consensus about the basic mechanisms and causes of rifting. The remarkable similarities in rift cross sections (shown in a figure), are considered to suggest that the anomalous lithospheric structure of rifts is more dependent on lithosphere properties than the mode of rifting. It is thought that there is a spectrum of rifting processes for which two fundamental mechanisms can be postulated: an active mechanism, whereby thermal energy is transmitted into the lithosphere from the underlying asthenosphere, and a passive mechanism by which mechanical energy is transmitted laterally through the lithosphere as a consequence of plate interactions at a distance. In order to permit the concept of the two fundamentally different mechanisms to be tested, a tentative classification is proposed that divides rifts into two basic categories: active rifting and passive rifting. Here, the magnitude of active rifting will depend on the rate at which lithosphere moves over the thermal source, with rifts being restricted to stationary or slow-moving plates.

Baker, B. H.↗
NASA NTRS1982

Relationships between the energetics of impulsive and gradual emissions from solar flares

The gradual soft X-ray emissions associated with a homogeneous set of solar flares have been investigated in the context of a thermal model proposed to explain the impulsive components. The parametric techniques which successfully characterized the hard X-ray and microwave observations are employed in an event-by-event analysis to test for quantitative and correlative relationships between the impulsive and gradual emissions. The results of this investigation are consistent with the hypothesis that the hard X-ray and microwave emissions are produced by bulk heating of a common thermal source. The quantitative relationships require an additional source to explain the soft X-ray observations, consistent with previous results. Correlations between the energetics of the impulsive and gradual emissions, identified in the present work, provide the first clear evidence that their energizing mechanisms are related.

Crannell, C. J.↗
NASA NTRS1982

HCMM hydrological analysis in Utah

The feasibility of applying a linear model to HCMM data in hopes of obtaining an accurate linear correlation was investigated. The relationship among HCMM sensed data surface temperature and red reflectivity on Utah Lake and water quality factors including algae concentrations, algae type, and nutrient and turbidity concentrations was established and evaluated. Correlation (composite) images of day infrared and reflectance imagery were assessed to determine if remote sensing offers the capability of using masses of accurate and comprehensive data in calculating evaporation. The effects of algae on temperature and evaporation were studied and the possibility of using satellite thermal data to locate areas within Utah Lake where significant thermal sources exist and areas of near surface groundwater was examined.

Miller, A. W.↗
NASA NTRS1984

The IRAS galaxy 0421+040P06: An active spiral (?) galaxy with extended radio lobes

The infrared bright galaxy 0421+040P06 detected by IRAS at 25 and 60 microns was studied at optical, infrared, and radio wavelength. It is a luminous galaxy with apparent spiral structure emitting 4 x 10 to the 37th power from far-infrared to optical wavelengths. Optical spectroscopy reveals a Seyfert 2 emission line spectrum, making 0421+040P06 the first active galaxy selected from an unbiased infrared survey of galaxies. The fact that this galaxy shows a flatter energy distribution with more 25 micron emission than other galaxies in the infrared sample may be related to the presence of an intense active nucleus. The radio observations reveal the presence of a non-thermal source that, at 6 cm, shows a prominent double lobed structure 20 to 30 kpc in size extending beyond the optical confines of the galaxy. The radio source is three to ten times larger than structures previously seen in spiral galaxies.

Beichman, C. A.↗
NASA NTRS1985

The IRAS galaxy 0421 + 040P06 - An active spiral (?) galaxy with extended radio lobes

The infrared bright galaxy 0421 + 040P06 detected by IRAS at 25 and 60 microns was studied at optical, infrared, and radio wavelength. It is a luminous galaxy with apparent spiral structure emitting 4 x 10 to the 37th power from far-infrared to optical wavelengths. Optical spectroscopy reveals a Seyfert 2 emission line spectrum, making 0421 + 040P06 the first active galaxy selected from an unbiased infrared survey of galaxies. The fact that this galaxy shows a flatter energy distribution with more 25 micron emission than other galaxies in the infrared sample may be related to the presence of an intense active nucleus. The radio observations reveal the presence of a non-thermal source that, at 6 cm, shows a prominent double lobed structure 20 to 30 kpc in size extending beyond the optical confines of the galaxy. The radio source is three to ten times larger than structures previously seen in spiral galaxies.

Beichman, C.↗
NASA NTRS1985

Absolute response and noise equivalent power of cyclotron resonance-assisted InSb detectors at submillimeter wavelengths

Spectra are presented of the responsivity and noise equivalent power (NEP) of liquid-helium-cooled InSb detectors as a function of magnetic field in the range 20-110 per cm. The measurements are all made using a Fourier transform spectrometer with thermal sources. The results show a discernable peak in the detector response at the conduction electron cyclotron resonance (CCR) frequency for magnetic fields as low as 3 kG. The magnitude of responsivity at the resonance peaks is roughly constant with magnetic field and is comparable to the low-frequency hot-electron bolometer response. The NEP at the peaks is found to be comparable to the best long wavelength results previously reported. For example, NEP = 4.5 x 10 to the 13th W/(square root of Hz) at 4.2 K, 6 kG, and 40 per cm was measured. The InSb CCR will provide a much improved detector for laboratory spectroscopy, as compared with hot electron bolometers, in the 20-100 per cm range.

Brown, E. R.↗
NASA NTRS1985

Evidence for supermassive stars in three Seyfert galaxy nuclei from IUE spectra

The variability in the ultraviolet continua and the C IV 1550 A emission profiles in the three Seyfert 1 galaxies NGC 4151, NGC 5548, and Fairall 9 are consistent with origin in supermassive stars undergoing explosive mass loss. Blackbody fits to continua of each imply a single thermal source whose area either remains constant or increases moderately as its temperature decreases, with the surface area consistent with stars having masses from 10 to the 6th to 10 to the 8th solar mass. Line emission profiles of C IV 1550 A in the same spectra are individually consistent with uniform expansion of shells of emitting gas expelled from the stars at radial velocities from 10,000 to 16,000 km/s. The kinetic energy removed by repetitive production of such massive shells approximately balances the nuclear energy production expected from supermassive stars of the indicated size. Finally, the observed nature and time scale of the variability of NGC 4151 is consistent with the relatively sudden appearance, and subsequent cooling, of the underlying superstellar surface as one such shell becomes transparent during its expansion.

Stoner, R.↗
NASA NTRS1986

The tail lobe ion spectrometer

A two-dimensional kinetic 'tail lobe ion spectrometer' model for the transport of ionospheric ions from polar cleft ionosphere into the tail lobes is developed to semiquantitatively simulate the behavior of the observed O(+) ion streams in the magnetotail lobes. The consequences of the present model include: (1) the increase in velocity of the O(+) streams away from the tail midplane; (2) the existence of 'tongues' of O(+) density from the cleft ionosphere into the tail lobes whose distribution configuration depends on the convection electric field and the source thermal energies; and (3) very low parallel thermal energies and speeds in the lobes which are correlated with the parallel ion bulk velocities. These consequences are reasonably consistent with the trends in lobe streams observed by recent spacecraft.

Horwitz, J. L.↗
NASA NTRS1987

Structural concepts for large solar concentrators

The Sunflower large solar concentrator, developed in the early 1970's, is a salient example of a high-efficiency concentrator. The newly emphasized needs for solar dynamic power on the Space Station and for large, lightweight thermal sources are outlined. Existing concepts for high efficiency reflector surfaces are examined with attention to accuracy needs for concentration rates of 1000 to 3000. Concepts using stiff reflector panels are deemed most likely to exhibit the long-term consistent accuracy necessary for low-orbit operation, particularly for the higher concentration ratios. Quantitative results are shown of the effects of surface errors for various concentration and focal-length diameter ratios. Cost effectiveness is discussed. Principal sources of high cost include the need for various dished panels for paraboloidal reflectors and the expense of ground testing and adjustment. A new configuration is presented addressing both problems, i.e., a deployable Pactruss backup structure with identical panels installed on the structure after deployment in space. Analytical results show that with reasonable pointing errors, this new concept is capable of concentration ratios greater than 2000.

Hedgepeth, John M.↗