Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Explanability”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Atmospheric storm explanation of saturnian electrostatic discharges

Saturn electrostatic discharges (SED) monitored by the Voyager 1 were investigated to determine the source of the phenomena. Consideration has been given to two sources: the atmosphere at equatorial latitudes, where the cloud-top wind velocities correspond to the Saturn 10 hr 10 min rotation period; and the rings at 1.8 Saturn radius. The data were analyzed in terms of time and frequency, revealing a time-varying frequency, few detectable discharges outside of a low threshold, and the appearances and disappearances of the SED with no correlation with frequency. The periodicity of the SED episodes indicated that the source was occulted between revolutions, which ruled out the ring source. The SED signals were only detected on the dayside, suggesting the signals propagated through the dayside ionosphere. Diurnal variations in the ion densities could prohibit the signals from escaping on the nightside, a factor supported by detection of low frequency SED only during close passage of the Voyager. Ray tracing experiments have demonstrated that storm sources have emissions observable with the storm on the limb at the observed 30-40 MHz interval.

Kaiser, M. L.↗
NASA NTRS1983

Explanation of the hypersonic longitudinal stability problem: Lessons learned

Inviscid and viscous CFD codes have been applied to a modified Space Shuttle orbiter geometry to investigate differences between preflight aerodynamic predictions and aerodynamic data from hypersonic reentry flight. Flow field solutions were obtained for wind tunnel conditions and flight conditions to assess Mach number, real-gas, and viscous effects on the reentry aerodynamics of the orbiter. Based on the CFD studies, a methodology model has been developed to (1) extrapolate wind tunnel data to flight conditions and (2) calculate a DCM for use with the Aerodynamic Design Data Book. Comparisons are made with selected flight data. Results of the study indicate that the differences between flight and pre-STS-1 predictions of hypersonic pitching moment are primarily due the to Mach number and real-gas effects.

Griffith, B. J.↗
NASA NTRS1983

A possible explanation for the present difference between linear noise theory and experimental data for supersonic helical tip speed propellers

High speed turboprops are attractive candidates for future aircraft because of their high propulsive efficiency. However, the noise of their propellers may create a cabin environment problem for the aircraft powered by these propellers. The noise of some propeller models was measured, and predictions of the noise using a method based on the Ffowcs Williams-Hawkins equation were made. The predictions and data agree well at lower helical tip Mach numbers but deviate above Mach 1.0. Some possible reasons why the theory does not predict the data and focuses on improvement of the aerodynamic inputs as the most likely remedy are investigated. In particular, it is proposed that an increase in the drag and a decrease in the lift near the tip of the blade where the majority of the noise is generated, is warranted in the input to the theory.

Dittmar, J. H.↗
NASA NTRS1982

A non-catastrophist explanation for the iridium anomaly at the Cretaceous/Tertiary boundary

The iridium (Ir) anomaly at the Cretaceous/Tertiary (C/T) boundary can be explained by dissolution of normal pelagic limestones producing an insoluble clay residue containing Ir-rich meteoritic material. Further concentration of Ir and other trace metals in the clay can be explained by deposition under reducing conditions. Clay-mineral analyses indicate that the boundary clay is similar to locally derived clays in the limestones above and below the boundary, and contains no detectable exotic components. This supports a terrestrial origin for the boundary clay. The genesis of the boundary clay is attributed to changes in ocean chemistry (pH and oxygenation), leading to an interval of widespread dissolution of carbonate sequences in the oceans, and culminating in the development of submarine pyritic hardgrounds and a disconformity of global extent.

Rampino, M. R.↗
NASA NTRS1984

Martian crater dark streak lengths - Explanation from wind tunnel experiments

The mechanism determining the length of dark erosional (type-Id) streaks near craters and hills on the surface of Mars is investigated using Mariner-9 images and the results of wind-tunnel studies (Greeley et al., 1974; Iversen et al., 1975 and 1976). An empirical model of time-dependent growth of crater-wake streaks in the downwind direction involving deflation by sand-grain saltation is developed and shown to give relatively good agreement with streak growth rates observed over a 38-day period of Mariner observations and with the streak-length/crater-diameter and streak-length/crater-height ratios analyzed statistically by Lee (1984). This time-dependent mechanism is thus considered a reasonable alternative (for dark streaks) to the blocking model proposed by Lee for both bright and dark streaks. Preliminary analysis of further wind-tunnel experiments (Iversen et al., 1982) supports the blocking model of bright-streak formation.

Iversen, J. D.↗
NASA NTRS1984

Explanation of the Normal Winter Anomaly from the Seasonal Variation of Short Wave Absorption

The frequency dependence of the winter anomaly (WA) of radio wave absorption indicates the altitude range where the considered seasonal variation of absorption, L, takes place: 75-95 km. In this height region considerable seasonal variations of ionic composition and effective recombination coefficient, alpha sub e, exist, which can cause seasonal variations of electron concentration, N, and absorption, L. An attempt to render a qualitative estimation of the normal WA, i.e., the increased ratio of winter over summer absorption, L sub w/L sub s, at medium latitudes 40 deg and 50 deg, for solar zenith angles CHi = 60 deg and 75 deg is made. This is compared with existing experimental data.

Velinov, P. J.↗
NASA NTRS1984

Solar-geophysical data number 479, August 1981. Part 2: (Comprehensive reports), data for January 1984 and August 1981 and miscellanea. Explanation of data reports issued as number 474 (supplement) February 1984

Various solar physical data are presented including: data for January 1984--(solar radio bursts af fixed frequencies, solar X-ray radiation from GOES satellite, Mass ejections from the sun); data for August 1981--solar flares; Miscellaneous data--(meudon carte synoptique, solar X-ray radiation from GOES satellite).

Coffey, H. E.↗
NASA NTRS1985

Explanation of the secondary to primary ratio within the continuous Fermi accelerator model

The secondary to primary ratio in galactic cosmic radiation at relativistic momenta is calculated in a model, where the primaries are continuously accelerated from the thermal galactic background medium by 1st and 2nd order Fermi acceleration. It is shown that the measured decrease with momentum does not exclude that cosmic rays are accelerated in the interstellar medium as a whole. Once a momentum dependence of the mean lifetime and the different spatial source distributions are adequately taken into account, the measured decreasing ratio can be explained.

Lerche, I.↗
NASA NTRS1984

Transitions in shallow convection - An explanation for lateral cell expansion

The generalized, seven-coefficient model presented for two-dimensional Rayleigh-Benard convection successfully simulates one way in which lateral cell expansion can occur as the value of the imposed vertical temperature difference is changed. The triad of interacting wavenumbers is varied as the vertical heating rate is varied and only the energetically active components are retained, so that transitional behavior within two-dimensional convective flow can be both simulated and physically interpreted as the representation of the cell expansion process via successive secondary branching. It is found that while a two-dimensional cell broadening mechanism is likely to operate for small Prandtl number values, a three-dimensional mechanism is expected at values greater than about 0.7.

Chang, H.-R.↗
NASA NTRS1985

Self-shielding in O2 - A possible explanation for oxygen isotopic anomalies in meteorites?

The production of isotopic effects in oxygen due to self-shielding of photolysing radiation by the Schumann-Runge bands of (O-16)2 is investigated. The model studied is the simple case of incoming radiation falling on a gaseous medium of uniform composition. The enhancement of O-17 and O-18 production upon photodissociation of O2 is calculated for various column densities, and its dependence on temperature and the presence of other molecules is examined. The issue of whether the products of photolysis can be trapped and thus preserve a peculiar isotopic composition is discussed.

Navon, O.↗
NASA NTRS1985

Explanation of the inward displacement of Io's hot plasma torus and consequences for sputtering sources

Radial profiles of the ion density and flux-tube content in the Io torus have peak values inside Io's orbit, even though Io is the effective source of these ions. Formation of an inward peak constrains either the velocity distributions or source regions of sputtered neutrals. A further constraint is that the ionization of neutrals on trapped trajectories that return to Io's surface must be limited. A dominant sulphur source is most easily reconciled with these constraints.

Linker, J. A.↗
NASA NTRS1986

Mode decoupling during retrorefraction as an explanation for bizarre radar echoes from icy moons

The two concepts of mode decoupling and retrorefraction are combined to explain the strength, distribution, and other features of the radar echoes from Europa, Ganymede, and Callisto. A decoupling of two characteristic modes of propagation appears to be a key to an understanding of the anomalous distribution of power among the polarized components of the echoes. Causes of the decoupling are proposed and their morphological implications are introduced.

Eshleman, V. R.↗
NASA NTRS1986

Possible explanation of the solar-neutrino puzzle

A new derivation of the Mikheyev and Smirnov (1985) mechanism for the conversion of electron neutrinos into mu neutrinos when traversing the sun is presented, and various hypotheses set forth. It is assumed that this process is responsible for the detection of fewer solar neutrinos than expected, with neutrinos below a minimum energy, E(m), being undetectable. E(m) is found to be about 6 MeV, and the difference of the squares of the respective neutrino masses is calculated to be 6 X 10 to the - 5th sq eV. A restriction on the neutrino mixing angle is assumed such that the change of density near the crossing point is adiabatic. It is predicted that no resonance conversion of neutrinos will occur in the dense core of supernovae, but conversion of electron neutrinos to mu neutrinos will occur as they escape outward through a density region around 100.

Bethe, H. A.↗
NASA NTRS1986

The upper atmosphere of Venus: A tentative explanation of its rotation

The upper atmosphere of Venus seems to revolve every 4 days, while the planet rotates in 243 days. Mariner 10 UV data on the changing positions of dark spots in the upper Venusian clouds have supported estimations of speeds ranging from 120-240 m/s. High rates of acceleration and deceleration occur on the night side, the former between -110 to -90 deg and the latter continuing to -50 deg. Arch and Y formations have been seen repeatedly between -110 to -70 deg. The highest are seen at about -90 deg and the lowest at about -30 deg. The temperature of the cloud layer at 60 km altitude is about 20 C, the pressure is nearly one earth atmosphere, and complex molecules, including O, C, H, N and S and combinations of these are present in abundance.

Boyer, C.↗
NASA NTRS1987

A possible explanation of the electron temperature enhancement in the wake of a satellite

A numerical simulation was performed in an attempt to explain the enhancement of electron temperature in the wake of an ionospheric satellite in terms of counterstreaming plasma expansions. The simulation was conducted using full kinetic treatments (Vlasov-Poisson code) for both the plasma electrons and ions. The calculations indicated that at a distance of a few Debye lengths from the surface of the body the wake/ambient electron-temperature ratio reaches a value of about 2. This result is in good agreement with some in situ and laboratory experimental results.

Singh, Nagendra↗
NASA NTRS1986

An explanation for the plateau phenomenon in isoelectric focusing

Isoelectric focusing of mixtures of simple ampholytes occurs in two phases, an initial rapid separation phase and a second relatively slow stabilizing phase. Transient and steady-state computer simulation data are shown to predict the development of pH plateaus around neutrality during the stabilizing phase of the focusing of such mixtures. This occurs because a nonzero electrophoretic flux is present in a pure zone of focused ampholyte, which is a function of both its isolectric point (pI) and its Delta-pK value. For an ampholyte with a pI greater than 9 or less than 5, this flux causes the development of a significant concentration gradient within its focused zone which is accompanied by a contraction of this zone along the focusing axis. Acidic and basic ampholytes are thereby displayed toward the anode and cathode respectively, creating a pH plateau in the neutral region. Thus, there will be regions of the focusing column, closer to the electrodes and containing more acidic or basic pH values, within which the resolution of samples will reach a maximum and then decrease.

Mosher, Richard A.↗
NASA NTRS1988

Expertise and reasoning with possibility: An explanation of modal logic and expert systems

Recently systems of modal reasoning have been brought to the foreground of artificial intelligence studies. The intuitive idea of research efforts in this area is that in addition to the actual world in which sentences have certain truth values there are other worlds in which those sentences have different truth values. Such alternative worlds can be considered as possible worlds, and an agent may or may not have access to some or all of them. This approach to reasoning can be valuable in extending the expert system paradigm. Using the scheme of reasoning proposed by Toulmin, Reike and Janick and the modal system T, a scheme is proposed for expert reasoning that mitigates some of the criticisms raised by Schank and Nickerson.

Rochowiak, Daniel↗