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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 271 records · Page 15
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NASA NTRS2010

Environmental Stress Testing of the Single Sample Cylinder: A Proven Consensus Standard for Internal Gas Analysis (IGA) or Residual Gas Analysis (RGA)

In August 2008, Schuessler Consulting was contracted by NASA GSFC in support of the NASA Electronic Parts and Packaging (NEPP) program to perform two separate studies on moisture laden air in a stainless steel cylinder that had been designed to become a consensus standard for Test Method 1018. This Test Method was originally released for hybrids under Mil. Std. 883 but was quickly utilized on other microelectronic devices under the auspice of Mil. Std. 750. The cylinder had subsequently been fabricated for the 750 community. It was back-filled with moist air and subsequently analyzed over a period of time under a previous NASA contract. It had been shown that moisture in the 4000 - 5000 ppm range could be analyzed rather precisely with a mass spectrometer, commonly referred to as a Residual Gas Analyzer (RGA). The scope of this study was to ascertain if the composition and precision varied as a function of thermal shock at sub-zero temperatures and whether there was consensus when the standard was submitted to other RGA units. It was demonstrated and published that the consensus standard would yield precise RGA data for moisture within +/- 1% when optimized for a given RGA unit. It has been subsequently shown in this study at Oneida Research Services, that sub-zero storage did not affect that precision when a well-defined protocol for the analysis was followed. The consensus standard was taken to a second facility for analysis where it was found that moisture adsorption on the transfer lines caused precision to drop to +/- 12%. The Single Sample Cylinder (SSC) is a one liter stainless steel cylinder with associated sampling valves and has considerable weight and volume. But this considerable size allows for approximately 300 gas samples of the same composition to be delivered to any RGA unit. Lastly, a smaller cylinder, approximately 75 cc, of a second consensus standard was fabricated and tested with a different mix of fixed gases where moisture was kept in the 100 ppm range. This second standard has the potential of providing 30 gaseous samples and can be readily shipped to any analytical facility that desires to generate comparison RGA data. A series of comparison residual gas analyses was performed at the Honeywell Federal Manufacturing & Technologies facility in the National Nuclear Facility Administration s plant in Kansas City to complete this project. It was shown that improvements in the precision of a given RGA unit can be done by controlling the cycle time for each analysis and increasing analysis temperatures to minimize moisture adsorption. It was also found that a "one time event" in the subzero storage of the large SSC did not effect the units ability to continuously supply precise samples of the same chemistry, however the "event" caused a permanent +8% shift in the reported value of the moisture content. Lastly, a set of SSC RGA results was plotted on a common graph with DSCC "correlation study" RGA data. The result demonstrates the ability of the SSC to remove many of the individual variances that single, individual samples introduce. The consensus standards are now in storage at Oneida Research Services, one of the DSCC certified houses that does RGA to Military Standards, where they await future studies. The analytical data and the operational parameters of the instruments used are provided in the following discussion. Limitations and suggested means for improvement of both precision and accuracy are provided.

Schuessler, Philipp WH↗
NASA NTRS1977

Turbulent scattering in an exponential atmosphere - A wave-optical solution

The thin-screen model for scattering of radiation by a turbulent atmosphere is generalized to the case where the mean phase change decreases exponentially as a function of distance across the screen. This is of interest because it models the effect of turbulent scattering in an isothermal average atmosphere. We present both the change in average intensity and average bending angle in terms of the r-m-s scattering angle introduced by the turbulence. We find, for example, that the effect of turbulent scattering on the mean scattering angle (and hence Doppler residuals) is approximately the same as that obtained from more heuristic calculations. The effect depends on wavelength only to the extent that the refractivity is a function of wavelength.

Hubbard, W. B.↗
NASA NTRS1987

Isotopic fractionation of Kr and Xe implanted in solids at very low energies

Results on the implantation of Kr and Xe in W under closed system conditions at very low energies (50-500 eV) are reported. Investigation of the fraction of gas trapped as a function of time reveals the existence of competing trapping and release mechanisms, and analysis of recovered trapped gas and residual gas phases shows that both elemental and isotropic fractionation result from these mechanisms. It is determined that the mass dependence for the overall implantation process is at or near m exp 1, with heavier isotopes enriched in the implanted gas. This mass dependence is inferred to result from implantation and a combination of diffusive and gas sputtering release mechanisms. These results reaffirm the conclusion of Bernatowicz and Fahey (1986) that previously observed isotopic fractionation of Kr and Xe in carbonaceous material synthesized in electrical discharges owes its origin to low-energy ion implantation, and also suggest that this process may be relevant to incorporation of noble gases in early solar system materials. The implication of these results for noble gas mass spectrometry are discussed.

Bernatowicz, Thomas J.↗
NASA NTRS1990

A Probable Approx. 2400 Year Solar Quasi-cycle in Atmospheric Delta C-14

A 2200 to 2600 year quasi-periodicity is present in atmospheric delta C-14 records after removal of long-term trends due to the geomagnetic dipole amplitude variation. This periodicity consists of both a long-term variation of the mean and a superposed, approximately recurring pattern of century-scale variations. The strongest of these latter variations occur near maxima of the approx. 2400 year delta C-14 cycles. The residual record can be modeled to first order as an amplitude modulation of a century-scale periodic forcing function by a approx. 2400 year periodic forcing function. During the last millennium, the largest century-scale variations (occurring near the most recent 2400 year delta C-14 maximum) are known to be mainly a consequence of the pronounced Maunder, Sporer, and Wolf solar activity minima, as verified by independent proxy solar activity records. Therefore, during this period, amplitude modulation has been occurring primarily in the sun and not in the terrestrial radiocarbon system. It is therefore inferred that the approx. 2400 year forcing function is mainly solar although some secondary terrestrial feedback into the delta C-14 record is likely. This conclusion has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.

Hood, L. L.↗
NASA NTRS2000

Timing Noise in SGR 1806-20

We have phase connected a sequence of Rossi X-ray Timing Explorer Proportional Counter Array observations of SGR 1806-20 covering 178 days. We find a simple secular spin-down model does not adequately fit the data. The period derivative varies gradually during the observations between 8.1 and 11.7 x 10(exp -11) s/s (approx. 40% larger than the long term trend), while the average burst rate as seen with the Burst and Transient Source Experiment drops throughout the time interval. The phase residuals show no evidence for periodicity, but more closely resemble timing noise as seen ill radio pulsars. The magnitude of the timing noise., however, is large relative to the noise level typically found in radio pulsars (Delta(sub 8) = 4.8; frequency derivative average power approx. = 8 X 10(exp -20) Hz/sq s). Combined with the noise levels measured for some AXPs. we find all magnetar candidates have A8 values larger than those expected from a simple extrapolation of the correlation found in radio pulsars. We find the timing noise ill SGR 1806-20 is greater than or equal to the levels found in some accreting systems (e.g., Vela X-1, 4U 1538-52 and 4U 1626-67). Alternatively, an orbital model with a period P(sub orb) = 733 days provides a statistically acceptable fit to the data. If the phase residuals are created by Doppler shifts from a gravitationally bound companion. then the allowed parameter space for the mass function (small) and orbital separation (large) rule out the possibility of accretion from the companion sufficient to power the persistent emission from the SGR.

Woods, Peter M.↗
NASA NTRS2000

Timing Noise in SGR 1806-20

We have phase-connected a sequence of Rossi X-Ray Timing Explorer Proportional Counter Array observations of SGR 1806-20 covering 178 days. We find that a simple secular spin-down model does not adequately fit the data. The period derivative varies gradually during the observations between 8.1 x 10(exp -11) and 11.7 x 10(exp -11) s/s (at its highest, approximately 40% larger than the long-term trend), while the average burst rate as seen with the Burst and Transient Source Experiment drops throughout the time interval. The phase residuals give no compelling evidence for periodicity, but more closely resemble timing noise as seen in radio pulsars. The magnitude of the timing noise, however, is large relative to the noise level typically found in radio pulsars (Delta(sub 8) = 4.8; frequency derivative average power approximately 7 x 10(exp -20) sq cycles/cubic s). Combining these results with the noise levels measured for some anomalous X-ray pulsars, we find that all magnetar candidates have Delta(sub 8) values larger than those expected from a simple extrapolation of the correlation found in radio pulsars. We find that the timing noise in SGR 1806-20 is greater than or equal to the levels found in some accreting systems (e.g., Vela X-1, 4U 1538-52, and 4U 1626-67), but the spin-down of SGR 1806-20 has thus far maintained coherence over 6 yr. Alternatively, an orbital model with a period P(sub orb) = 733 days provides a statistically acceptable fit to the data. If the phase residuals are created by Doppler shifts from a gravitationally bound companion, then the allowed parameter space for the mass function (small) and orbital separation (large) rule out the possibility of accretion from the companion sufficient to power the persistent emission from the SGR.

Woods, P. M.↗
NASA NTRS2019

Local frustration around enzyme active sites

Conflicting biological goals often meet in the specification of protein sequences for structure and function. Overall, strong energetic conflicts are minimized in folded native states according to the principle of minimal frustration, so that a sequence can spontaneously fold, but local violations of this principle open up the possibility to encode the complex energy landscapes that are required for active biological functions. We survey the local energetic frustration patterns of all protein enzymes with known structures and experimentally annotated catalytic residues. In agreement with previous hypotheses, the catalytic sites themselves are often highly frustrated regardless of the protein oligomeric state, overall topology, and enzymatic class. At the same time a secondary shell of more weakly frustrated interactions surrounds the catalytic site itself. We evaluate the conservation of these energetic signatures in various family members of major enzyme classes, showing that local frustration is evolutionarily more conserved than the primary structure itself.

Maria I. Freiberger↗
NASA NTRS1988

Estimating residual fault hitting rates by recapture sampling

For the recapture debugging design introduced by Nayak (1988) the problem of estimating the hitting rates of the faults remaining in the system is considered. In the context of a conditional likelihood, moment estimators are derived and are shown to be asymptotically normal and fully efficient. Fixed sample properties of the moment estimators are compared, through simulation, with those of the conditional maximum likelihood estimators. Properties of the conditional model are investigated such as the asymptotic distribution of linear functions of the fault hitting frequencies and a representation of the full data vector in terms of a sequence of independent random vectors. It is assumed that the residual hitting rates follow a log linear rate model and that the testing process is truncated when the gaps between the detection of new errors exceed a fixed amount of time.

Lee, Larry↗
NASA NTRS2017

Sugar Derivatives in Residues Produced from the UV Irradiation of Astrophysical Ice Analogs

A large variety of organic compounds of astrobiological and prebiotic interest have been detected in carbonaceous meteorites. These include amino acids, carboxylic acids, amphiphiles, functionalized nitrogen heterocycles such as nucleobases, functionalized polycylic aromatic hydrocarbons such as quinones, and sugar derivatives. The sugar derivatives identified in the Murchison and Murray meteorites are mainly sugar alcohols and sugar acids, and only the smallest sugar (dihydroxyacetone) has been detected. The presence of such a variety of organics in meteorites strongly suggests that molecules essential to life can form abiotically under astrophysical conditions. This hypothesis is further supported by laboratory studies in which astrophysical ice analogs (mixtures of H2O, CO, CO2, CH3OH, CH4, NH3, etc.) are subjected to ultraviolet (UV) irradiation at low temperature (<15 K) to simulate cold interstellar environments. These studies show that the organic residues recovered at room temperature after irradiation contain amino acids, amphiphiles, nucleobases, sugar derivatives, as well as other complex organic compounds. The finding of such compounds under plausible interstellar conditions is consistent with the presence of organic compounds in meteorites. Until very recently, no systematic search for the presence of sugar derivatives in laboratory residues had been carried out. The detection of ribose, the sugar constituent of RNA in all living systems, as well as other sugars, sugar alcohols, and sugar acids have been recently reported in one organic residue produced from the UV irradiation of an H2O:CH3OH:NH3 (10:3.5:1) ice mixture at 80 K. In this work, we present a detailed study of organic residues produced from the UV irradiation ice mixtures of several starting compositions (containing H2O, CH3OH, CO, CO2, and/or NH3) at <15 K for their sugar derivative content. Our results confirm the presence of all 3C‒5C sugar alcohols, several 3C‒5C sugars, and all 3C‒4C sugar acids (in decreasing order of abundances) in the residues. The higher abundances of sugar alcohols in these residues suggest a pathway in which sugar alcohols are formed first, while the formation of sugars and sugar acids require more steps. Finally, our results are compared with the detection of sugars derivatives in primitive meteorites.

Astrophysical Ice Analogs↗
NASA NTRS1972

Study of the detail content of Apollo orbital photography

The results achieved during a study of the Detail Content of Apollo Orbital Photography are reported. The effect of residual motion smear or image reproduction processes upon the detail content of lunar surface imagery obtained from the orbiting command module are assessed. Data and conclusions obtained from the Apollo 8, 12, 14 and 15 missions are included. For the Apollo 8, 12 and 14 missions, the bracket-mounted Hasselblad camera had no mechanism internal to the camera for motion compensation. If the motion of the command module were left totally uncompensated, these photographs would exhibit a ground smear varying from 12 to 27 meters depending upon the focal length of the lens and the exposure time. During the photographic sequences motion compensation was attempted by firing the attitude control system of the spacecraft at a rate to compensate for the motion relative to the lunar surface. The residual smear occurring in selected frames of imagery was assessed using edge analyses methods to obtain and achieved modulation transfer function (MTF) which was compared to a baseline MTF.

Kinzly, R. E.↗
NASA NTRS1986

Effect of texture on magnetoacoustic stress measurement in steel

The effect of texture on the general stress measurements of a heavily cold rolled steel plate is analyzed. Changes in the acoustic natural velocity for plate samples with their long axes perpendicular, parallel, and in a 40 degree direction with respect to the rolling axis were measured; graphs of the velocity variations for the three samples are provided. It is observed that the negative minimum change in the acoustic natural velocity under residual compression for the perpendicular sample is about half that of the parallel and 40 degree samples indicating that the functional form of the velocity curve is influenced by the structural properties of the sample; however, the stress measurements are unaffected by the texture.

Namkung, M.↗
NASA NTRS1987

Dislocation dynamics and the viscoplastic buckling of dendritic web type silicon ribbon

The effect of dendrites (reinforced edges) on the residual stresses, dislocation densities and buckling behavior during growth of web type silicon ribbon is studied. A viscoplastic material response function (Haasen-Sumino model) is used to calculate the stresses and the disloction density at each point in the silicon ribbon. In addition, the role of dendrites on the viscoplastic buckling behavior of the ribbon is investigated. The critical thicknesses, the corresponding deflection shapes and lateral deflection speeds are calculated. These results are then compared with similar data obtained for flat plates.

Tsai, C. T.↗
NASA NTRS1989

Proton irradiation of SiH4-Fe(CO)5-H2O ices - Production of refractory silicates and implications for the solar nebula

The results of a number of experiments are reported in which SiH4-Fe(CO)5-H2O ice mixtures were irradiated by 1 MeV protons at 15 K and then warmed to room temperature in approximately 50 K steps. The properties of a sample were monitored by observing its infrared absorption spectrum as a function of its processing history. In each experiment in which ice samples containing SiH4 were irradiated, a refractory amorphous silicate residue remained after warming to room temperature. In addition to the usual broad silicate features at 10 and 20 microns, features due to water or hydroxyl at 3 and 6.2 microns, and a feature due to CO at 5 microns, a surprisingly stable infrared feature at 4.6 microns, attributed to the SiH stretching fundamental, was observed.

Nuth, J. A.↗
NASA NTRS2007

Lightning Charge Retrievals: Dimensional Reduction, LDAR Constraints, and a First Comparison with LIS Satellite Data

A "dimensional reduction" (DR) method is introduced for analyzing lightning field changes (DELTAEs) whereby the number of unknowns in a discrete two-charge model is reduced from the standard eight (x, y, z, Q, x', y', z', Q') to just four (x, y, z, Q). The four unknowns (x, y, z, Q) are found by performing a numerical minimization of a chi-square function. At each step of the minimization, an Overdetermined Fixed Matrix (OFM) method is used to immediately retrieve the best "residual source" (x', y', z', Q'), given the values of (x, y, z, Q). In this way, all 8 parameters (x, y, z, Q, x', y', z', Q') are found, yet a numerical search of only 4 parameters (x, y, z, Q) is required. The DR method has been used to analyze lightning-caused DeltaEs derived from multiple ground-based electric field measurements at the NASA Kennedy Space Center (KSC) and USAF Eastern Range (ER). The accuracy of the DR method has been assessed by comparing retrievals with data provided by the Lightning Detection And Ranging (LDAR) system at the KSC-ER, and from least squares error estimation theory, and the method is shown to be a useful "stand-alone" charge retrieval tool. Since more than one charge distribution describes a finite set of DELTAEs (i.e., solutions are non-unique), and since there can exist appreciable differences in the physical characteristics of these solutions, not all DR solutions are physically acceptable. Hence, an alternative and more accurate method of analysis is introduced that uses LDAR data to constrain the geometry of the charge solutions, thereby removing physically unacceptable retrievals. The charge solutions derived from this method are shown to compare well with independent satellite- and ground-based observations of lightning in several Florida storms.

Koshak, W. J.↗
NASA NTRS2007

Lightning Charge Retrievals: Dimensional Reduction, LDAR Constraints, and a First Comparison w/ LIS Satellite Data

A "dimensional reduction" (DR) method is introduced for analyzing lightning field changes whereby the number of unknowns in a discrete two-charge model is reduced from the standard eight to just four. The four unknowns are found by performing a numerical minimization of a chi-squared goodness-of-fit function. At each step of the minimization, an Overdetermined Fixed Matrix (OFM) method is used to immediately retrieve the best "residual source". In this way, all 8 parameters are found, yet a numerical search of only 4 parameters is required. The inversion method is applied to the understanding of lightning charge retrievals. The accuracy of the DR method has been assessed by comparing retrievals with data provided by the Lightning Detection And Ranging (LDAR) instrument. Because lightning effectively deposits charge within thundercloud charge centers and because LDAR traces the geometrical development of the lightning channel with high precision, the LDAR data provides an ideal constraint for finding the best model charge solutions. In particular, LDAR data can be used to help determine both the horizontal and vertical positions of the model charges, thereby eliminating dipole ambiguities. The results of the LDAR-constrained charge retrieval method have been compared to the locations of optical pulses/flash locations detected by the Lightning Imaging Sensor (LIS).

Koshak, William↗
NASA NTRS2007

Lightning Charge Retrievals: Dimensional Reduction, LDAR Constraints, and a First Comparison with LIS Satellite Data

A "dimensional reduction" ("DR") method is introduced for analyzing lightning field changes ((Delta)Es) whereby the number of unknowns in a discrete two-charge model is reduced from the standard eight (x, y, z, Q, x', y', z', Q') to just four (x, y, z, Q). The four unknowns (x, y, z, Q) are found by performing a numerical minimization of a chi-square function. At each step of the minimization, an overdetermined fixed matrix (OFM) method is used to immediately retrieve the best "residual source" (x', y', z', Q'), given the values of (x, y, z, Q). In this way, all eight parameters Ix. y, z, Q, x', y', z', Q') are found, yet a numerical search of only four parameters (x, y, z, Q) is required. The DR method has been used to analyze lightning-caused (Delta)Es derived from multiple ground-based electric field measurements at the NASA Kennedy Space Center (KSC) and U.S. Air Force Eastern Range (ER). The accuracy of the DR method has been assessed by comparing retrievals with data provided by the lightning detection and ranging (LDAR) system at the KSC-ER. and from least squares error estimation theory, and the method is shown to be a useful "stand alone" charge retrieval tool. Since more than one charge distribution describes a finite set of (Delta)Es (i.e., solutions are nonunique), and since there can be appreciable differences in the physical characteristics of these solutions, not all DR solutions are physically acceptable. Hence. an alternative and more accurate method of analysis is introduced that uses LDAR data to constrain the geometry of the charge solutions. thereby removing physically unacceptable retrievals. The charge solutions derived from this method are shown to compare well with independent satellite- and ground-based observations of lightning m several Florida storms.

Koshak, W. J.↗
NASA NTRS2014

Development Status of Adjustable Grazing Incidence Optics for 0.5 Arcsecond X-Ray Imaging

We describe progress in the development of adjustable grazing incidence X-ray optics for 0.5 arcsec resolution cosmic X-ray imaging. To date, no optics technology is available to blend high resolution imaging like the Chandra X-ray Observatory, with square meter collecting area. Our approach to achieve these goals simultaneously is to directly deposit thin film piezoelectric actuators on the back surface of thin, lightweight Wolter-I or Wolter- Schwarschild mirror segments. The actuators are used to correct mirror figure errors due to fabrication, mounting and alignment, using calibration and a one-time figure adjustment on the ground. If necessary, it will also be possible to correct for residual gravity release and thermal effects on-orbit. In this paper we discuss our most recent results measuring influence functions of the piezoelectric actuators using a Shack-Hartmann wavefront sensor. We describe accelerated and real-time lifetime testing of the piezoelectric material, and we also discuss changes to, and recent results of, our simulations of mirror correction.

Reid, Paul B.↗
NASA NTRS2015

Tropical Simultaneous Nadir Observations for IR Sounder Evaluation and Comparison

Simultaneous Nadir Observations (SNOs) contain thousands of pairs of observations taken within 8 km and 10 minutes. SNOs have been very useful for comparisons in polar conditions. But classic SNO pairing criteria have very low yield in the tropics, making these SNOs less useful for investigating instrument performance for hotter scenes or scenes with high contrast. We introduce a modified methodology, which finds pairs of matched spectra in a wider angular range but is restricted to the tropics. We illustrate this with AIRS and CrIS data. Insight into instrument differences is gained from statistical distributions of the residual differences between the matched pairs. A sample analysis compares AIRS and CrIS brightness temperature at 900 cm-1 as function of scene brightness temperature. The proposed method may be applicable to matchups of other sensors on different spacecraft.

AIRS↗