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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Big Bang nucleosynthesis and the Quark-Hadron transition

An examination and brief review is made of the effects of quark-hadron transistion induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp 3), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Kurki-Suonio, Hannu↗
NASA NTRS1989

Sensory conflict in motion sickness: An observer theory approach

Motion sickness is the general term describing a group of common nausea syndromes originally attributed to motion-induced cerebral ischemia, stimulation of abdominal organ afferent, or overstimulation of the vestibular organs of the inner ear. Sea-, car-, and airsicknesses are the most commonly experienced examples. However, the discovery of other variants such as Cinerama-, flight simulator-, spectacle-, and space sickness in which the physical motion of the head and body is normal or absent has led to a succession of sensory conflict theories which offer a more comprehensive etiologic perspective. Implicit in the conflict theory is the hypothesis that neutral and/or humoral signals originate in regions of the brain subversing spatial orientation, and that these signals somehow traverse to other centers mediating sickness symptoms. Unfortunately, the present understanding of the neurophysiological basis of motion sickness is far from complete. No sensory conflict neuron or process has yet been physiologically identified. To what extent can the existing theory be reconciled with current knowledge of the physiology and pharmacology of nausea and vomiting. The stimuli which causes sickness, synthesizes a contemporary Observer Theory view of the Sensory Conflict hypothesis are reviewed, and a revised model for the dynamic coupling between the putative conflict signals and nausea magnitude estimates is presented. The use of quantitative models for sensory conflict offers a possible new approach to improving the design of visual and motion systems for flight simulators and other virtual environment display systems.

Oman, Charles M.↗
NASA NTRS1989

Evidence from the limb infrared monitor of the stratosphere for nonlocal thermodynamic equilibrium in the nu2 mode of mesospheric water vapour and the nu3 mode of stratospheric nitrogen dioxide

Data from the 6.9-micron H2O channel and the 6.2-micron NO2 channel of the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) have been used to investigate the daytime enhancement to H2O; the high concentration of H2O sometimes observed in the polar night mesosphere; and the high ratio of daytime to nighttime NO2 in the upper stratosphere. These three phenomena deviate noticeably from the predictions of photochemical theory. The 20 to 30 percent diurnal variation in stratospheric H2O apparent in LIMS data cannot be reconciled with a photochemical lifetime in excess of four months. This is attributed to departure from local thermodynamic equilibrium of daytime emission which had not been accounted for in retrievals. Speculative possibilities of NLTE emission from the H2O nu2 and NO2 nu3 hot bands are discussed. It is found that the nonthermal emission from NO2 significantly affects retrieval of H2O in the polar nighttime and NO2 in the daytime stratosphere at low latitudes.

Kerridge, Brian J.↗
NASA NTRS1990

A test of the galactic origin of gamma-ray bursts

Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for up to 10 to the 10th yr. Other calculations included the dipole moment in the angular distribution of neutron stars as a convenient measure of their concentration toward the Galactic center, the quadrupole moment in their angular distribution as a convenient measure of their concentration toward the Galactic plane, and the average value of V/Vmax as a convenient measure of the radial distribution of neutron stars. Models that require accretion from a cold circumstellar disk or from a close companion are only marginally consistent with the isotropic distribution of the observed bursts. Models that require accretion of interstellar matter are ruled out due to a very strong dipole anisotropy. Models that suggest the Galactic halo origin of gamma-ray bursts are briefly discussed. The GRANAT and GRO missions should provide evidence for or against the association of gamma-ray bursts with the Galactic disk neutron stars.

Paczynski, Bohdan↗
NASA NTRS1989

Geochemistry of polymict ureilite EET83309, and a partially-disruptive impact model for ureilite origin

Bulk-compositional data for the EET83309 polymict ureilite were obtained using INAA and radiochemistry procedures and electron probe analysis. It was found that the EET83309 has a bulk composition indistinguishable from ordinary ('monomict') ureilites for all elements except light-middle REEs (which are present in much higher concentrations), suggesting that polymict ureilites are mixtures of ordinary ureilites which were mixed on a very small number of parent bodies. Despite the light-REE enrichments, polymict ureilites are nearly devoid of basaltic (Al-rich) material. It is suggested that the missing basalt may have been blown off the parent body by a partially disruptive collision with a large C-rich projectile. This impact model of ureilite origin reconciles many paradoxical aspects of ureilite composition.

Warren, Paul H.↗
NASA NTRS1990

An IRAS survey of the Taurus-Auriga molecular cloud

IRAS data are used to search for young premain-sequence stars not previously associated with molecular cloud cores in the Taurus-Auriga region. NIR photometry and optical spectroscopy suggest that many of the objects are young stars. The sample includes six new embedded sources with luminosities comparable to that of the average T Tauri star, suggesting that surveys for premain-sequence stars in the cloud are essentially complete for luminosities greater than 0.5 solar luminosities. A disagreement is found between accretion rates derived from the duration of the embedded phase and those derived from the bolometric luminosity. It is found that this disagreement may be reconciled if a star accretes most of its mass in a time that is short compared to the duration of the embedded phase or if the ages of T Tauri stars have been underestimated.

Kenyon, Scott J.↗
NASA NTRS1990

Big bang nucleosynthesis and the quark-hadron transition

An examination and brief review is made of the effects of quark-hadron transition induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp e), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Kurki-Suonio, Hannu↗
NASA NTRS1990

Imaging spectroscopy of Mars (0.4-1.1 micron) during the 1988 opposition

The paper presents imaging spectroscopic data and preliminary interpretations acquired during the 1988 perihelic opposition of Mars at the highest spatial resolution achieved from earth for spectrometric measurements (all contiguous spatial sampling for nearly 70 percent of the planet) and at a higher spectral resolution (R = 350) than most previous measurements in the (0.4-1.1)-micron wavelength range. Absorption features appearing near 0.6-0.7 and 0.80-0.95 micron are attributed to Fe(3+) crystal field transitions, confirming previously made measurements at lower spectral resolution. It is shown that attempts to reconcile the overall spectral shape with those of laboratory minerals or Mars analog soils spectra affirm the recent interpretations that hematite may account for nearly all of the 18 wt pct Fe2O3 measured by Viking Landers.

Bell, J. F., III↗
NASA NTRS1990

Thermodynamic aspects of heat pipe operation

An expanded heat pipe operating model is described which includes thermodynamic and heat transfer considerations to reconcile disparities between actual and theoretical heat pipe performances. The analysis shows that thermodynamic considerations can explain the observed heat pipe performance limitations. A full understanding of thermodynamic processes could lead to advanced concepts for thermal transport devices.

Richter, Robert↗
NASA NTRS1990

Jovian H2 dayglow emission (1978-1989)

The IUE data set accumulated through 10 years of Jovian equatorial observations is used to measure the long-term temporal variation of the H2 dayglow emission. The model that best fits the data indicates a possible correlation between long-term solar activity and the Jovian H2 emission in the region 1500-1700 A between 1978 and 1989, which spans the decline in solar activity for solar cycle 21 and the rise in solar activity accompanying solar cycle 22. The magnitude of the observed variation is closer to that of the solar Ly-alpha flux than the 10.7 cm radio flux. Short-wavelength H2 band emission intensity is inconsistent with the amount of long-wavelength emission but may be reconciled if relatively low-energy excitation or fluorescence of solar radiation is invoked. No persistent longitudinal feature analogous to the H I Ly-alpha can be identified.

Mcgrath, M. A.↗
NASA NTRS1990

Vertical distribution of water in the atmosphere of Venus - A simple thermochemical explanation

Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to strikingly unusual distributions (the water vapor abundance decreases sharply in the immediate vicinity of the surface) or to serious conflicts in the profiles (different IR bands suggest water abundances that are discrepant by a factor of 2.5 to 10). These data sets can be reconciled if (1) water molecules associate with carbon dioxide and sulfur trioxide to make gaseous carbonic acid and sulfuric acid in the lower atmosphere, and (2) the discrepant 0.94-micrometer water measurements are due to gaseous sulfuric acid, requiring it to be a somewhat stronger absorber than water vapor in this wavelength region. A mean total water abundance of 50 + or - 20 parts/million and a near-surface free water vapor abundance of 10 + or - 4 parts/million are derived.

Lewis, John S.↗
NASA NTRS1990

Bremsstrahlung X-rays from Jovian auroral electrons

The spectrum of X-rays from the planet Jupiter is calculated according to an auroral electron beam model. The electrons are assumed to be accelerated by a field-aligned potential drop and penetrate into the atmosphere as a Maxwellian beam of primaries which are scattered, degraded in energy, and merged with a population of ionization secondaries having a power law energy distribution. The soft X-rays observed by the Einstein Observatory satellite are due to bremsstrahlung from the secondary electrons in the H2 atmosphere. The X-ray intensity is best reconciled with a beam of primaries having a characteristic energy 30-100 keV and penetrating the homopause with an auroral energy flux typically of 10-20 ergs/sq cm s but no greater than 50 ergs/sq cm s.

Barbosa, D. D.↗
NASA NTRS1990

0108 + 388 - A compact double source with surprising properties

49 cm, 6 cm, and 20 cm observations of the compact double ratio source 0108 + 388 are presented. Extended emission about 20 deg to the east of the core is detected which resembles a hot spot/lobe with a bridge of emission extending back to the core. This is the first detection of extended emission associated with such a source, and it is inconsistent with the suggestion that such sources are very young classical double radio sources. The inconsistency can be reconciled if the activity in this object is recurrent and the emission is the relic of a previous epoch of activity. Alternatively, the source may be a normal-aged radio galaxy in which most of the radio-emitting plasma is currently unable to escape the nuclear regions of the galaxy. The steep low-frequency spectrum of the core is probably related to the origin of the compact double and suggests that both components are very sharply confined on both their inner and outer edges.

Baum, S. A.↗
NASA NTRS1990

The Triton torus revisited

Prior to the Voyager encounter with Neptune, Delitsky et al. (1989) predicted that a torus of ions emanating from Triton would be discovered. These predictions are reexamined in light of the Voyager results. Sputtering of Triton's atmosphere can produce the heavy ion densities inferred at Triton's orbit by the Voyager plasma experiment if the ion residence time is about 30 days. The torus is found to be longitudinally asymmetric near Triton, with peak densities at longitudes of 170 and 350 deg. The total nitrogen flux due to sputtering is about 2 x 10 to the 21st/s. The consequences of larger escape fluxes of both N2 and H2 are investigated; it is difficult to reconcile large escape fluxes with the plasma and ultraviolet spectrometer observations.

Richardson, John D.↗
NASA NTRS1990

Zonally averaged thermal balance and stability models for nitrogen polar caps on Triton

Voyager four-color imaging data of Triton are analyzed to calculate the bolometric hemispheric albedo as a function of latitude and longitude. Zonal averages of these data have been incorporated into a thermal balance model involving insolation, reradiation, and latent heat of sublimation of N2 ice for the surface. The current average bolometric albedo of Triton's polar caps is 0.8, implying an effective temperature of 34.2 K and a surface pressure of N2 of 1.6 microbar for unit emissivity. This pressure is an order of magnitude lower than the surface pressure of 18 microbar inferred from Voyager data (Broadfoot et al., 1989; Conrath et al., 1989), a discrepancy that can be reconciled if the emissivity of the N2 on Triton's surface is 0.66. The model predicts that Triton's surface north of 15 deg N latitude is experiencing deposition of N2 frosts, as are the bright portions of the south polar cap near the equator. This result explains why the south cap covers nearly the entire southern hemisphere of Triton.

Stansberry, John A.↗
NASA NTRS1991

Using fuzzy logic to integrate neural networks and knowledge-based systems

Outlined here is a novel hybrid architecture that uses fuzzy logic to integrate neural networks and knowledge-based systems. The author's approach offers important synergistic benefits to neural nets, approximate reasoning, and symbolic processing. Fuzzy inference rules extend symbolic systems with approximate reasoning capabilities, which are used for integrating and interpreting the outputs of neural networks. The symbolic system captures meta-level information about neural networks and defines its interaction with neural networks through a set of control tasks. Fuzzy action rules provide a robust mechanism for recognizing the situations in which neural networks require certain control actions. The neural nets, on the other hand, offer flexible classification and adaptive learning capabilities, which are crucial for dynamic and noisy environments. By combining neural nets and symbolic systems at their system levels through the use of fuzzy logic, the author's approach alleviates current difficulties in reconciling differences between low-level data processing mechanisms of neural nets and artificial intelligence systems.

Yen, John↗
NASA NTRS1991

Sensitivity-based scaling for correlating structural response from different analytical models

A sensitivity-based linearly varying scale factor is described used to reconcile results from refined models for analysis of the same structure. The improved accuracy of the linear scale factor compared to a constant scale factor as well as the commonly used tangent approximation is demonstrated. A wing box structure is used as an example, with displacements, stresses, and frequencies correlated. The linear scale factor could permit the use of a simplified model in an optimization procedure during preliminary design to approximate the response given by a refined model over a considerable range of design changes.

Chang, Kwan J.↗
NASA NTRS1990

Small-scale disequilibrium in a magmatic inclusion and its more silicic host

An investigation of small-scale isotopic, compositional, and mineralogical variation across the interface of a basaltic-andesite inclusion and its dacitic host from Cerro-Chascon, a Holocene dome in northern Chile, is discussed. Serial sectioning across the interface of the inclusion and its host dacite, complemented by microdrill sampling and detailed microprobe work, has enabled an examination of the scale of mixing and chemical disequilibrium. The composition of the inclusion is found to be relatively homogeneous; the dacite host is heterogeneous on a small scale; the isotopic composition in the marginal zone shows the highest Sr-87/Sr-86 and lowest Nd-143/Nd-144; the large plagioclase crystals in the inclusions and host are xenocrystic. These differences are reconciled with a model of magma evolution in a crustal magma chamber.

Davidson, Jon P.↗