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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Results from cascade thrust reverser noise and suppression experiments

Results from experimental work on model scale cascade reversers with cold airflow are presented. Sound power levels, directivity, and spectral characteristics for cascade reversers are reported. Effect of cascade exit area ratio, vane profile shape, and emission arc are discussed. Model equivalent diameters varied from 3 to 5 inches; pressure ratios ranged from 1.15 to 3.0. Depending on the reverser type, acoustic power was proportional to the 4.5- to 6-th power of ideal jet velocity. Reverser noise peaked at higher frequency and was more omnidirectional than nozzle-alone jet noise. Appreciable reduction in sideline noise was obtained from plane shields.

Gutierrez, O. A.↗
NASA NTRS1973

Some correlations between measurements by the Apollo gamma-ray spectrometer and other lunar observations

Observations by the Apollo 15 and 16 gamma-ray spectrometers are compared with those of a number of other experiments, both compositional and noncompositional. A general correspondence with topography is seen. The Van de Graaff area is a unique farside region with respect to observations by the laser altimeter, the subsatellite magnetometer, and the gamma-ray spectrometer. X-ray and alpha particle orbital measurements show a broad general agreement with gamma-ray data, although results from additional elements in the gamma-ray spectrum are needed to extend the comparison with X-ray data. A comparison of Th concentrations with those found at various landing sites shows generally good agreement, with the orbital values tending to be somewhat higher.

Trombka, J. I.↗
NASA NTRS1974

Jupiter's ionosphere - Prospects for Pioneer 10

Model Jovian ionospheres are constructed for comparison with Pioneer 10 results. Electron density maxima are predicted at a level approximately 220 kilometers above an assumed reference height where the hydrogen density is 10 to the 16-th power molecules per cubic centimeter. It may be possible to use observations of the electron density to locate the turbopause. Attention is drawn to a possible strong source of ionized sodium from Io which might lead to large electron densities at low altitudes.

Atreya, S. K.↗
NASA NTRS1974

Interplanetary diffusion coefficients for cosmic rays

Information on the cosmic-ray diffusion coefficient, kappa, derived from near-earth observations of the solar modulation of galactic electron fluxes and from the near-earth power spectra of the interplanetary magnetic field, has been used to study the heliocentric radial dependence of kappa, and to derive limits on the spatial extent of the solar modulation region. Representing kappa, as a separable function of radius r and rigidity, and assumming kappa(r) proportional to r to the n-th power, we can place a limit on the power law exponent, n not greater than 1.2. The distance of the modulation boundary is a function of n, and, e.g., for n = 0, falls into the range of 6-25 AU.

Cummings, A. C.↗
NASA NTRS1974

Hydraulic concentration of magnetic fields in the solar photosphere. I - Turbulent pumping

Observations suggest that most of the magnetic flux through the solar photosphere is concentrated in vertical filaments in the supergranule boundaries. Each filament appears to contain about 3 times 10 to the 18-th power maxwells, in the form of a field of 500 gauss or more, over a diameter of 700 km or less. The magnetic energy density in the filaments is 100 times the observed kinetic energy density of the observed supergranule motions, but comparable to the kinetic energy density of the granules. Force-free field configurations cannot duplicate the observational numbers, nor can such cooling effects as are believed responsible for the intense fields in sunspot umbrae. We point out a simple hydraulic mechanism (turbulent pumping) that appears to account for the observed concentration of fields.

Parker, E. N.↗
NASA NTRS1974

OSO-7 observations of a high-latitude X-ray source associated with Abell cluster A2052

An X-ray source with a flux of 1.6 times 10 to the -10th power ergs per sec/sq cm (2-10 keV) has been observed at high galactic latitude by the MIT X-ray detectors on the OSO-7 satellite. Designated GX 8+50, its position is 15 hr 14.2 min right ascension, 6 deg 51 min declination, with a 90 percent confidence error circle of area 0.5 sq deg. The data are consistent with a power-law spectrum with an exponent 1.2 (plus or minus 0.2) or a thermal-bremsstrahlung spectrum with kT = 4 plus or minus 1 keV. A likely identification is the Abell cluster A2052, whose center coincides with the radio source 3C 317.

Heinz, C. J.↗
NASA NTRS1974

On ionization in H I regions

A comparison is made of the K I, Na I, Ca II, and H I interstellar absorption lines formed in relatively low-density interstellar clouds in H I regions. The data indicate that the fractional ionization (ratio of electron density to hydrogen density) is nearly constant for a range in hydrogen densities covering a factor of 15. If ionization balance exists in the clouds, then ionization of hydrogen by either low-energy cosmic rays or soft X-rays cannot be the principal source of the observed free electrons, and the hydrogen ionization rate is less than 10 to the -16th power per sec for these processes.

Hobbs, L. M.↗
NASA NTRS1973

Chemistry of the moon's surface

The chemical composition of the lunar surface is discussed on the basis of analyses of Apollo samples. Three new minerals, armalcolite, pyroxferroite and tranquillityite, high abundances of Ti, Zr, Sr, Y, Nb, U and Th, and a predominance of radiogenic isotopes of Pb are noted as the prominent features unraveled by sample analysis. Evidence is indicated to support the conclusion that the lunar rocks investigated are products of partial fusion and magmatic crystallization modified in much of the material by mechanical breakup and shock melting, and containing a small amount of meteoritic material. It is inferred from the results that the surface rocks are igneous in origin and that the moon has been a passive object since 3000 million years ago.

Mason, B.↗
NASA NTRS1974

Decomposition-aggregation stability analysis of the spinning Skylab

Stability of an 11-th order linear model of the spinning Skylab is determined by the decomposition-aggregation method based upon the comparison principle and vector Liapunov functions. To reduce the inherent conservativeness of the method an optimization problem is formulated and resolved producing the optimum comparison system. The system provides the best estimate of the stability region of the important structural parameter - asymmetry in the boom settings.

Cuk, S. M.↗
NASA NTRS1974

Gamma-spectrometric analysis of Luna 16 sample of lunar surface material

Using a scintillation gamma spectrometer with shielding against anticoincidences, the content of the natural radioelements (K, U, and Th) and long-lived cosmogenic radioisotopes (Al-26, Na-22, and Mn-54) in a sample of Sea of Fertility regolith was determined. Based on the content data of natural radioelements, an attempt was made to classify this sample in the scale of petrochemical types of terrestrial rocks arranged in accordance with their silicic content and alkalinity. Within the frame of reference of calcium-uranium systematics of lunar samples, a comparison was made of the K/U ratio obtained for the Sea of Fertility sample with analogous data for other regions of the moon. Also discussed are problems on the depthwise distribution of cosmogenic radioisotopes along the regolith profile.

Surkov, Y. A.↗
NASA NTRS1974

Formation and composition of the moon

Many of the properties of the moon are discussed including the enrichment in Ca, Al, Ti, U, Th, Ba, Sr and the REE and the depletion in Fe, Rb, K, Na and other volatiles which could be understood if the moon represents a high temperature condensate from the solar nebula. Thermodynamic calculations show that Ca, Al and Ti rich compounds condense first in a cooling nebula. The initial high temperature mineralogy is gehlenite, spinel, perovskite, Ca-Al-rich pyroxenes and anorthite. Inclusions in Type III carbonaceous chondrites such as the Allende meteorite are composed primarily of these minerals and, in addition, are highly enriched in refractories such as REE relative to carbonaceous chondrites. These inclusions can yield basalt and anorthosite in the proportions required to eliminate the europium anomaly, leaving a residual spinel-melilite interior.

Anderson, D. L.↗
NASA NTRS1974

Lunar elemental analysis obtained from the Apollo gamma-ray and X-ray remote sensing experiment

Gamma ray and X-ray spectrometers carried in the service module of the Apollo 15 and 16 spacecraft were employed for compositional mapping of the lunar surface. The measurements involved the observation of the intensity and characteristics energy distribution of gamma rays and X-rays emitted from the lunar surface. A large scale compositional map of over 10 percent of the lunar surface was obtained from an analysis of the observed spectra. The objective of the X-ray experiment was to measure the K spectral lines from Mg, Al, and Si. Spectra were obtained and the data were reduced to Al/Si and Mg/Si intensity ratios and ultimately to chemical ratios. The objective of the gamma-ray experiment was to measure the natural and cosmic ray induced activity emission spectrum. At this time, the elemental abundances for Th, U, K, Fe, Ti, Si, and O have been determined over a number of major lunar regions.

Trombka, J. I.↗
NASA NTRS1974

X-ray structure of the Cygnus loop

An X-ray surface brightness map of the Cygnus Loop in the energy range 0.15-0.85 keV is presented. The X-ray distribution is compared with the optical and radio pictures of the Loop. The location of the center of the supernova shell as derived from the X-ray data is in excellent agreement with the apparent optical and radio centers. We obtain a mean diameter for the X-ray shell of 2.75 (+ or - 0.2) deg. The X-ray spectral data yield a characteristic thermal temperature averaged over the Loop of 2.9 million (+ or - 1.5 million) K. We have calculated anew X-ray parameters for adiabatic blast waves using X-ray production spectra which include line radiation. These parameters are compared with the results of the present experiment. An age of 18,000 years, initial blast energy equal to 3 times 10 to the 50-th power ergs, and ambient interstellar density of 0.25 per cu cm are found.

Rappaport, S.↗
NASA NTRS1974

Stability properties of functional difference equations

Hale and Cruz (1970) have defined the concept of a stable difference operator, and have found that this class of operators is sometimes 'super sensitive' to perturbations. In the present paper, a subclass of general functional difference equations is derived which retain their stability under appropriate perturbations. Also, the results of Hale and Cruz are extended to include difference equations on the Banach space of p-th power integrable functions, and essentially bounded functions.

Melvin, W. R.↗
NASA NTRS1974

Alternant codes

A class of codes defined by the parity check matrix of a linear code of minimum distance at least t + 1 is examined and the number of parity check symbols is discussed. Determinants of this type are known as alternants (Muir and Metzler, 1930); codes corresponding to such a matrix are termed alternant codes. The parity check matrix is obtained by restricting some of its elements to subfields of GF(q to the m-th power). Minimum distance and redundancy bounds are established for these codes, and some interesting equivalence and invariance properties are derived.

Helgert, H. J.↗
NASA NTRS1975

Al-26 in cores of the Keyes chondrite

Radionuclide concentration data for six samples from two cores of the Keyes chondrite are presented. The weighted average potassium content for samples was about 675 ppm, somewhat lower than the 800-900 ppm typically found in L chondrites. Spectra were analyzed for U and Th, with upper limits established at approximately 100 and 200 ppb, respectively.

Cressy, P. J.↗