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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 523 records · Page 29

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NASA NTRS1974

Some effects of diffusion on the flow of ions in the solar wind

The contribution of diffusive effects to the near equality of flow velocities of H+ and heavier ions of the solar wind at 1 AU is examined. Frictional drag on heavy ions from average solar wind fluxes of H+ appears to make an appreciable contribution to equalizing velocities. The frictional drag on H+ due to the presence of heavy ions may make an appreciable contribution to equalizing flow velocities, since compensating increases in coronal temperatures may be required in order to give solar wind velocities for H+. However, rather large enhancements of heavy ions near the sun appear to be required. If appreciable enhancements of heavy ions extend beyond about 2.5 solar radii, significant increases in heavy ion temperatures above H+ temperatures may be produced. This temperature difference may contribute to equalizing flow velocities and may contribute to the explanation of measured temperature differences at 1 AU between H+ and He++.

Nakada, M. P.↗

NASA NTRS1974

Low-altitude acceleration of auroral electrons during breakup observed by a mother-daughter rocket

By the use of a mother-daughter rocket combination and ground-based observations with television, time and space variations are resolved in particle measurements in breakup aurora. The spectral variations measured during a temporal variation in the aurora can be explained by a nearly uniform acceleration of all the electrons such as would be caused by an electric potential drop along the magnetic field lines. Many other explanations can be eliminated.

Johnstone, A. D.↗

NASA NTRS1974

Fractionation of moderately volatile elements in ordinary chondrites

The CI chondrites are the most volatile-rich meteorites. Relative to the CI chondrites, the ordinary chondrites have lower abundances of refractory and volatile elements. Four types of fractionations are summarized in a table. Ordinary-chondrite/CI abundance ratios for moderately volatile elements in H- and L-group chondrites are presented in a graph. Possible explanations for the observed relations are considered, giving attention to several processes which could result in the separation of nebular solids and gases.

Wasson, J. T.↗

NASA NTRS1974

Crystallization of dense neutron matter

The equation of state for cold neutron matter at high density is studied in the t-matrix formulation, and it is shown that energetically it is convenient to have neutrons in a crystalline configuration rather than in a liquid state for values of the density exceeding 1600 Tg/cu cm. The study of the mechanical properties indicates that the system is stable against shearing stresses. A solid core in the deep interior of heavy neutron stars appears to offer the most plausible explanation of speed-ups observed in the Vela pulsar.

Canuto, V.↗

NASA NTRS1974

Satellites and magnetospheres of the outer planets

The known properties of the satellites of the outer planets are reviewed and an attempt is made to provide explanations for some of the more striking features in terms of interaction with the planetary magnetospheres. It is pointed out that all the larger satellites, with the exception of Iapetus, are likely to lie within the magnetospheres of their respective planets at all times. Attention is given to the possibility that the satellites and other solid bodies situated within the planetary magnetospheres become charged to rather large electrical potentials. Satellite brightness variations are considered together with the atmospheres of the satellites.

Mendis, D. A.↗

NASA NTRS1974

The interstellar depletion mystery, or where have all those atoms gone

The observed depletion of intermediate-weight elements O, C, and N from the interstellar medium is shown to be significantly greater than can be accounted for by accretion on interstellar dust. A number of possible explanations are presented, ranging from the existence in interstellar space of many 'snowballs' intermediate in size between dust grains and comets to the existence of many far more complicated interstellar molecules than have been detected.

Greenberg, J. M.↗

NASA NTRS1974

Investigation of acoustic effects of leading-edge serrations on airfoils

This paper presents and interprets a series of extensive studies of the application of leading-edge serrations as a device for reducing the vortex noise radiated from stationary and rotating airfoils in low Reynolds number flow. In these studies, a variety of serrations were attached at selected locations near the leading edge of stationary and rotating airfoils. The noise levels of the airfoils were reduced considerably with the serrations attached. An explanation of the aeroacoustic flow mechanisms involved is given.

Hersh, A. S.↗

NASA NTRS1974

Auroral particle precipitation and Birkeland currents

Correlated measurements that provide information on Birkeland (field aligned) currents are reviewed. Because of the obvious importance of field-aligned electric fields with regard to Birkeland currents, the last section of the paper is devoted to a presentation of recent data on the observations of field-aligned auroral electron fluxes and monoenergetic peaks in the spectrum. Experimental data cannot yet define the overall magnetospheric pattern of the Birkeland current system. The largest body of data regarding these currents comes from polar-orbiting satellites. These data indicate that current sheets are associated with auroral displays and that field-aligned electron fluxes on the order of 1-keV energy are significant charge carriers for the conventional current out of the atmosphere. Rocket observations verify that electrons responsible for the production of auroral forms carry a significant fraction of the current necessary to produce local magnetic effects that require Birkeland currents for their explanations.

Arnoldy, R. L.↗

NASA NTRS1974

Generation of Alfven waves in the magnetosphere by parametric interaction between whistlers

A theory is developed for the generation of Alfven waves by the mixing of whistler waves. Calculations are carried out for interaction in the magnetosphere where the whistlers fall in the VLF frequency range and the Alfven wave falls in the ULF(1-5 Hz) range. Typical amplitudes of 2-5 milligammas for the Alfven wave are calculated, and it is shown that these values might be increased by one order of magnitude through suitable variation of the experimental parameters. The study thereby develops a possible explanation for naturally occurring Pc 1 micropulsations and demonstrates the feasibility of artificial generation of such micropulsations by ground-launched whistlers.

Harker, K. J.↗

NASA NTRS1974

Change of blaze wavelength as a function of position on the surface of a concave grating

Conventional ruling of a concave diffraction grating with blaze angle constant relative to the optical axis produces a grating whose blaze wavelength changes continuously with displacement across the face of the ruled area. A simple explanation of the effect is given in terms of geometrical optics, and quantitative expressions are developed that relate the expected blaze-wavelength shift to the grating constant and aperture ratio. Results are compared with experimental efficiency measurements, and the magnitude of the effect in a typical grating is discussed.

Michels, D. J.↗

NASA NTRS1974

Time variation of the H2O maser and infrared continuum in late-type stars

Observations of the variability of the 1.35-cm H2O and 2.2-micron emission from eight late M stars are described. A comparison of the microwave and infrared variations is of interest because the bulk of the stellar energy is radiated in the near-infrared and because at least one theory (Litvak 1969) hypothesizes near-infrared maser pumping via the 2.7-micron H2O vibration-rotation band. Variations at the two wavelengths appear to be correlated and possible explanations for this correlation are discussed.

Schwartz, P. R.↗

NASA NTRS1974

Infrared variability of V1016 Cygni

Infrared data obtained from broad-band photometric observations on the 60-inch telescope of the Hale observatories on Mount Wilson with the Becklin-Neugebauer photometer are discussed. The infrared magnitudes (shown as a function of time) illustrate the periodic nature of the V1016 Cygni variations. In particular, it can be seen that the longer-wavelength IR emission between 3 and 10 microns varies along with the shorter-wavelength emission. Although other explanations are possible, the infrared variability and luminosity of V1016 Cyg suggests the presence of Mira variable component together with the hot component now seen visually.

Harvey, P. M.↗

NASA NTRS1974

Hydrocortisone and ACTH levels in manned spaceflight

The plasma hydrocortisone, plasma ACTH, and urinary hydrocortisone values were recorded for each man of the crews of Apollo flights eight through fifteen, 30, 14, and 5 days before flight, immediately after spaceflight recovery, and on future days until the return of most variables to preflight values. The plasma and urinary preflight hydrocortisone values were significantly higher than the postflight values. This result is discussed in terms of three possible explanations: (1) the adrenal-cortical function is suppressed during spaceflight; (2) the activity in flight may amount to stressful exercise, which tests have shown can cause a decrease in plasma adrenocortical hormones; and (3) the in-flight work-rest cycles may be such as to affect the circadian periodicity of the pituitary-adrenal function.

Leach, C. S.↗

NASA NTRS1974

Some new aspects on the superrotation of the thermosphere

The motion of the thermosphere with a rotational velocity between 10 and 20 per cent in excess of the earth's rotational velocity has been deduced by King-Hele and his co-workers from the change of the inclination of satellite orbits. To date, no completely satisfactory explanation of the observations has been presented. In this paper, it is shown that in the thermosphere there exists a small diurnal mean driving force in the eastward direction. This force has not previously been considered in analyses of superrotation. A critical review of the observations and a theoretical analysis that takes account of both equinox and solstice conditions is presented. In the lower height region, where the great majority of observations were made, it is possible to achieve agreement between observations and a dynamical model. Additional observational data are needed in the isothermal region for a more complete analysis.

Blum, P. W.↗

NASA NTRS1974

On the breakup of tectonic plates by polar wandering

The equations for the stresses in a homogeneous shell of uniform thickness caused by a shift of the axis of rotation are derived. The magnitude of these stresses reaches a maximum value of the order of 10 to the 9th power dyn/sq cm, which is sufficient for explaining a tectonic breakup. In order to deduce the fracture pattern according to which the breakup of tectonic plates can be expected the theory of plastic deformation of shells is applied. The analysis of this pattern gives an explanation of the existing boundary systems of the major tectonic plates as described by Morgan (1968), LePichon (1968) and Isacks et al. (1968).

Liu, H.-S.↗

NASA NTRS1974

Large-amplitude hydromagnetic waves

Several aspects of the theory of large-amplitude hydromagnetic waves and their behavior in the interplanetary medium are examined. The characteristic modes of the full (i.e., nonlinearized) MHD equations and their modification by collisionless and finite-frequency effects are considered. Special attention is paid to the transverse Alfven mode, which is undamped and characterized by strictly constant pressure, density, and B; this seems to be the predominant propagating fluctuation at 1 AU. It is shown that its propagation in the small-wavelength (WKB) approximation is essentially identical to that of the small-amplitude Alfven wave of linearized theory. It is also suggested that its presence at 1 AU may provide a natural explanation of the observed power anisotropy of the fluctuations. A second-order analysis is used to study fluctuations that are not characteristic modes. It is found that for a small range of propagation directions, and subject to third-order effects, a finite-amplitude wave can exist that is linearly polarized with delta B perpendicular to both B sub zero and k; such a wave can damp nonlinearly.

Barnes, A.↗

NASA NTRS1974

Variable features on Mars. IV - Pavonis Mons

A remarkable set of albedo changes has been uncovered by Mariner 9 photography of the upper slopes of the shield volcano Pavonis Mons, near its summit caldera. The most likely explanation of the event is aeolian transport of fine-grained particles. Since the atmospheric pressure in this locality is about 1.5 mb, minimum wind velocities above the surface boundary layer of about 110 m per sec are necessary, corresponding to 0.51 of the speed of sound. Slope winds in this velocity range are expected near the upper flanks of major Martian volcanic constructs.

Sagan, C.↗

NASA NTRS1974

Radial and directional solidification of metallic systems in space

Investigation of the solidification behavior of spherical specimens of Ni-12 wt % Sn and Ni-1 wt % Ag that froze radially from the surface toward the center and cylindrical specimens of Al-33 wt % Cu eutectic that froze directionally under appropriately selected conditions of thermal gradient at the solid-liquid interface and growth rate. Possible effects of vacuum and low gravity conditions, under which the spherical specimens were processed, on observed nucleation and growth phenomena are discussed. A genetic explanation is given of observed microstructures, and the distributions of alloying elements is discussed. In directionally solidified eutectic specimens a comparison is made between statistically evaluated growth defects in Skylab and in ground specimens.

Katamis, T. Z.↗