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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Magnetohydrodynamic thermal instabilities in cool inhomogeneous atmospheres

The stability of magnetic loops to current-driven filamentation instabilities is investigated. The unperturbed atmosphere is assumed to be composed of an (upper) isothermal optically thin low-density portion and a (lower) higher-density portion which is in radiative equilibrium; in both cases, the atmosphere is in hydrostatic equilibrium, so that gravitational stratification is taken into account. In order to provide specific equilibrium conditions for evaluation of the dispersion relation, conditions appropriate for the surface of a solar-type star are adopted; i.e., a fairly low temperature (T = 5000 K) appropriate for a 'precoronal' state associated, for example, with magnetic flux emerging from photospheric levels under the action of magnetic buoyancy. A linear stability analysis is performed, and numerical results show that physically plausible current densities, which would be generated by typical loop-footpoint motions, are effective in driving MHD instabilities in such a plasma. The instability growth rates are strongly dependent on the assumed current density distribution and on the density scale height.

Bodo, G.↗
NASA NTRS1966

Density of an exosphere.

Density distribution in exosphere, particularly Maxwellian velocity distribution disturbed by light particle escape

DENSITY DISTRIBUTION↗
NASA NTRS1985

A tomographic technique for aerodynamics at transonic speeds

Computer aided tomography (CAT) provides a means of noninvasively measuring the air density distribution around an aerodynamic model. This technique is global in that a large portion of the flow field can be measured. A test of the applicability of CAT to transonic velocities was studied. A hemispherical-nose cylinder afterbody model was tested at a Mach number of 0.8 with a new laser holographic interferometer at the 2- by 2-Foot Transonic Wind Tunnel. Holograms of the flow field were taken and were reconstructed into interferograms. The fringe distribution (a measure of the local densities) was digitized for subsequent data reduction. A computer program based on the Fourier-transform technique was developed to convert the fringe distribution into three-dimensional densities around the model. Theoretical aerodynamic densities were calculated for evaluating and assessing the accuracy of the data obtained from the tomographic method.

Lee, G.↗
NASA NTRS1985

A tomographic technique for aerodynamics at transonic speeds

Computer aided tomography (CAT) provides a means of noninvasively measuring the air density distribution around an aerodynamic model. This technique is global in that a large portion of the flow field can be measured. A test of the applicability of CAT to transonic velocities was studied. A hemispherical-nose cylinder afterbody model was tested at a Mach number of 0.8 with a new laser holographic interferometer at the 2- by 2-Foot Transonic Wind Tunnel. Holograms of the flow field were taken and were reconstructed into interferograms. The fringe distribution (a measure of the local densities) was digitized for subsequent data reduction. A computer program based on the Fourier-transform technique was developed to convert the fringe distribution into three-dimensional densities around the model. Theoretical aerodynamic densities were calculated for evaluating and assessing the accuracy of the data obtained from the tomographic method.

Lee, G.↗
NASA NTRS1966

Computer experiments on electron guns.

Cathode current density distribution, beam minimum radius and location and electrode current interception, using computer techniques on electron guns

CATHODE↗
NASA NTRS1990

Radial profiles of gas in late-type disk galaxies

The azimuthally averaged neutral hydrogen (HI) distribution, and the total gas density distribution derived from HI and CO observations (N sub H2 = 2.8 x 10(exp 20) I sub CO) as a function of radius in several nearby, early-type disks are examined.

Struck-Marcell, Curtis↗
NASA NTRS2018

3D Mapping of the Neutral X-Ray Absorption in the Local Interstellar Medium: The Gaia and XMM-Newton Synergy

We present a three-dimensional map of the hydrogen density distribution in the Galactic interstellar medium. The hydrogen-equivalent column densities were obtained from the Exploring the X-ray Transient and variable Sky project (EXTRAS) which provides equivalent NH values from X-ray spectral fits of observations within the XMM-Newton Data Release. EXTRAS include multiple fits for each source, allowing an accurate determination of the equivalent column densities, which depends on the continuum modelling of the spectra. A cross-correlation between the EXTRAS catalogue and the first Gaia Data Release was performed in order to obtain accurate parallax and distance measurements. We use a Bayesian method explained in Rezaei Kh. et al. (2017) in order to predict the most probable distribution of the density at any arbitrary point, even for lines of sight along which there are no initial observation. The resulting map shows small-scale density structures which could not have been modelled by using analytic density profiles. In this paper, we present a proof of concept of the kind of science possible with the synergy of these catalogues. However, given the systematic uncertainties connected to the source identification and to the dependence of NH on the spectral model, the present maps should be considered qualitatively at this point.

Gatuzz, Efrain↗
NASA NTRS1967

Electrodynamics of media

Electrodynamics of media, emphasizing obtaining expressions for macroscopic force density distribution

DENSITY DISTRIBUTION↗
NASA NTRS1974

The evolution of electron density and temperature distributions in the topside ionosphere during magnetic storms

The latitudinal distributions of electron density and temperature during geomagnetic storms in the mid-latitude topside ionosphere are observed to change in a manner than can be related to the evolution of ring current particle populations. The region of auroral precipitation is characterized by correlated increases in electron temperature and density. Equatorwards of this region, there is a broad belt of elevated electron temperatures and depressed electron densities which is usually much broader than any stable auroral red arc distinguishable from the ground, but which is nevertheless the same basic physical phenomenon. The changes of position of this belt can be related to prior bursts of geomagnetic activity and injection of ring current particles into the magnetosphere.

Cole, K. D.↗
NASA NTRS1974

Mercury - Internal structure and thermal evolution

Mercury's thermal evolution and internal structure are modeled based on the planet's gross physical properties (which imply a high metallic iron content) and predictions for its chemistry made from the Lewis-Cameron model of condensation of the primitive solar nebula (which implies that Mercury may be composed only of those materials that condensed at temperatures near that of metallic iron condensation in the cooling nebula). Various heat sources, initial temperatures, and thermal conductivities are considered for a homogeneous model and a differentiated two-layer model. Density distributions are calculated from the mean density and estimates of the present-day temperature. The moment of inertia and the hydrostatic value of the second degree harmonic coefficient of Mercury's gravity field are found for the differentiated and undifferentiated models. These results should be useful for preliminary interpretation of the Mariner 10 measurements of Mercury's gravitational field.

Siegfried, R. W., II↗