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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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364 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Impact experiments in viscous fluid media

Available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy, anelastic dispersion, sphericity, and gravity. The resulting models, for average Earth, average ocean, and oceanic regions divided according to the age of the ocean floor, are quite different from previous results which ignore the above effects. The models show a low-veocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studied. The correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive. For most of the Earth SHSV in the vicinity of the low-velocity zone. Near the East Pacific Rise, however, SVSH at depth, consistent with ascending flow. Anisotropy is as important as temperature in causing radial and lateral variations in velocity. The models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age. This layer defines the LID, or seismic lithosphere. In the Pacific, the LID thickens with age to a maximum thickness of about 50 km. This thickness is comparable to the thickness of the elastic lithosphere. The LID thickness is thinner than derived using isotropic or pseudo-isotropic procedures A new model for Average Earth is obtained which includes a thin LID. This model extends the fit of a P.R.E.M. type model to shorter period surface waves.

Greeley, R.↗
NASA NTRS2009

A Model of Thermal Conductivity for Planetary Soils: Theory for Cemented Soils - 2

A numerical model of heat conduction through particulate media made of spherical grains cemented by various bonding agents is presented. The pore-filling gas conductivity, volume fraction, and thermal conductivity of the cementing phase are tunable parameters. Cement fractions <0.001-0.01% in volume have small effects on the soil bulk thermal conductivity. A significant conductivity increase (factor 3-8) is observed for bond fractions of 0.01 to 1% in volume. In the 1 to 15% bond fraction domain, the conductivity increases continuously but less intensely (25-100% conductivity increase compared to a 1% bond system). Beyond 15% of cements, the conductivity increases vigorously and the bulk conductivity rapidly approaches that of bedrock. The composition of the cements (i.e. conductivity) has little influence on the bulk thermal inertia of the soil, especially if the volume of bond <10%. These results indicate that temperature measurements are sufficient to detect cemented soils and quantify the amount of cementing phase, but the mineralogical nature of the bonds and the typical grain size are unlikely to be determined from orbit. On Mars, a widespread surface unit characterized by a medium albedo (0.19-0.26) and medium/high thermal inertia (200-600 J s(0.5)/sq m/K) has long been hypothesized to be associated with a duricrust. The fraction of cement required to fit the thermal data is less than approx.1-5% by volume. This small amount of material is consistent with orbital observations, confirming that soil cementation is an important factor controlling the thermal inertia of the Martian surface

Piqueux, S.↗
NASA NTRS1990

Velocity-Resolved Far-Infrared Spectra of [Fe 2]: Evidence for Mixing and Clumping in SN 1987A

We present approx. 400 km/s resolution profiles of the 17.94 and 25.99 micron [Fe II] transitions from SN 1987A at t approx. 400 days after core collapse. These observations used the facility cooled grating spectrometer aboard NASA's Kuiper Airborne Observatory. The two profiles are similar and have FWHM line widths of approx. 2700 km/s. The higher signal-to-noise 18 micron profile is somewhat asymmetric, falling off more steeply on the redshifted side than on the blue. Gaussian fits to the profiles yield an average centroid velocity of 280 +/- 140 km/s relative to the Large Magellanic Cloud. The wings of the profiles extend to velocities is approx. greater than 3000 km/s. This shows that a significant fraction of the iron has been mixed outward into the hydrogen-rich envelope, which has a minimum expansion velocity of 2100-2400 km/s. Both profiles also contain an unresolved 3-5 sigma emission feature on the redshifted wing at nu(LSR) approx. + 3900 km/s. We interpret this feature as emission from a high-velocity clump of material containing approx. 3% of the total iron mass. The total line flux of the 26 micron ground-state transition yields an optically thin, singly ionized iron mass of 0.026 solar mass, relatively independent of the assumed temperature. This is significantly less than the 0.06 Me of Fe+ determined from the decline of the optical light curve and the ionization of measured nickel lines, implying that the iron transitions still have appreciable optical depth. However, because of the small change in the 26 micron line flux from our measurement at 250 days, and the similarity of our profiles to the 1.26 micron [Fe II] profile, most of the emission is believed to originate from optically thin material with a temperature of 4406 +/- 400 K. A comparison of the data with spherically symmetric models indicates a power-law density exponent of -3.2 +/- 1.1 and a minimum expansion velocity of 650 +/- 650 km/s for this optically thin component. The [Fe II] line fluxes and profiles also imply that the remainder of the material has high optical depth and is distributed in clumps throughout the ejecta, rather than being concentrated at low velocities in the center of a smooth density distribution.

Haas, Michael R.↗
DOE OSTI2021

Skyrme pseudopotentials at next-to-next-to-leading order: Construction of local densities and first symmetry-breaking calculations

There is an ongoing quest to improve on the spectroscopic quality of nuclear energy density functionals (EDFs) of the Skyrme type through extensions of its traditional form. One direction for such activities is the inclusion of terms of higher order in gradients in the EDF. We report on exploratory symmetry-breaking calculations performed for an extension of the Skyrme EDF that includes central terms with four gradients at next-to-next-to-leading order (N2LO) and for which the high-quality parametrization SN2LO1 has been constructed recently. Up to now, the investigation of such functionals with higher-order terms was limited to infinite matter and spherically symmetric configurations of singly and doubly magic nuclei. We address here nuclei and phenomena that require us to consider axial and nonaxial deformation, both for reflection-symmetric and also reflection-asymmetric shapes, as well as the breaking of time-reversal invariance. Achieving these calculations demanded a number of formal developments. These all resulted from the formulation of the N2LO EDF requiring the introduction of new local densities with additional gradients that are not present in the EDF at NLO. Their choice is not unique, but can differ in the way the gradients are coupled. While designing a numerical implementation of N2LO EDFs in Cartesian three-dimensional coordinate-space representation, we have developed a novel definition and a new unifying notation for normal and pair densities that contain gradients at arbitrary order. Besides having mnemonic advantages, the new notation allows for the easy identification of redundancies and reducibilities in a given set of local densities, and the new definition makes it straightforward to construct densities that automatically adopt the symmetries of the many-body state they are constructed from. The resulting scheme resolves several issues with some of the choices that have been made for local densities in the past, in particular when breaking time-reversal symmetry. Guided by general practical considerations, we propose an alternative form of the N2LO contribution to the Skyrme EDF that is built from a different set of densities. It has exactly the same physics content, but is much more efficient to handle in formal discussions and, compared to the original formulation, leads to a substantial reduction of computational cost and memory requirements in deformed codes. As representative examples for the performance of SN2LO1, we have chosen the ground states of even-even Kr and Nd isotopes, the fission barrier of 240 Pu as well as the superdeformed rotational band of 194 Hg. Overall, for the nuclei and phenomena studied here, the SN2LO1 parametrization does not yet present a systematic improvement over standard NLO parametrizations. This finding calls for improved fit protocols that better discriminate between NLO and N2LO terms and better exploit the unique features of the additional degrees of freedom offered by the latter.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗