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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Further observations of the 10830-A helium line in stars and their significance as a measure of stellar activity

Measurements of the 10830-A He line in 198 stars are given along with data on other features in that spectral range. Nearly 80 per cent of all G and K stars show some 10830-A absorption or emission; of these, half are variable and one-quarter show emission. The results of Vaughan and Zirin (1968) are confirmed that the 10830-A line is not found in M stars, is weak in F stars, and is particularly strong in close binaries. The line is found in emission in extremely late M and S stars along with P-gamma, but the latter is not in emission in the G and K stars with 10830-A emissions. Variable He emission along with Ti I emission is found in the RV Tauri variables R Sct and U Mon. In R Aqr, the Fe XIII coronal line at 10747 A is found in emission along with a line at 11012 A, which may be singlet He or La II, as well as the 10830-A and P-gamma lines. There is possibly a five-year period in the appearance of 10830-A emission in theta Her. The nature of coronae or hot chromospheres in the various stars is extensively discussed without definite conclusion, except that the 10830-A intensity must be more or less proportional to the energy deposited in the chromosphere-corona by nonthermal processes.

Zirin, H.↗
NASA NTRS1976

Isotopic composition of the Martian atmosphere

Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of earth. Mars is enriched in N-15 relative to earth by about 75 per cent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO2 or H2O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of O-18.

Nier, A. O.↗
NASA NTRS1976

The atmosphere of Mars near the surface - Isotope ratios and upper limits on noble gases

Several analyses of the Martian atmosphere have been carried out with the mass spectrometer in the molecular-analysis experiment. The ratios of abundant isotopes of carbon and oxygen are within 10 per cent of terrestrial values, whereas nitrogen-15 is considerably enriched on Mars. Argon-38 has been detected, and new limits on abundances of krypton and xenon have been set. The limit on krypton is sufficiently low to suggest that the inventories of volatile substances on Mars and on earth may be distinctly different.

Biemann, K.↗
NASA NTRS1976

Viking magnetic properties investigation - Preliminary results

Three permanent-magnet arrays are aboard the Viking lander. By sol 35, one array, fixed on a photometric reference test chart on top of the lander, has clearly attracted magnetic particles from airborne dust; two other magnet arrays, one strong and one weak, incorporated in the backhoe of the surface sampler, have both extracted considerable magnetic mineral from the surface as a result of nine insertions associated with sample acquisition. The loose Martian surface material around the landing site is judged to contain 3 to 7 per cent highly magnetic mineral which, pending spectrophotometric study, is thought to be mainly magnetite.

Hargraves, R. B.↗
NASA NTRS1976

Jupiter's spectrum between 12 and 24 micrometers

Spectroscopic measurements of the thermal radiation from Jupiter between 12 and 24 micrometers (420 to 840 reciprocal centimeters) with a resolution of 4 reciprocal centimeters are used to infer the Jovian temperature structure in the pressure region from 0.1 to 0.4 atmosphere. The brightness-temperature spectrum is in good agreement with previous ground-based measurements between 11 and 13 micrometers and with airborne measurements between 18 and 25 micrometers. However, the integrated flux calculated for a filter window and viewing angle equivalent to those of the 20-micrometer channel of Pioneer 10 is 20 per cent below that measured by the Pioneer infrared radiometer. The Q branch of the nu-5 fundamental band of acetylene at 730 reciprocal centimeters appears in emission and leads to a mixing-ratio estimate of 10 to the -6th (plus or minus 0.5) power.

Aumann, H. H.↗
NASA NTRS1976

Neutral hydrogen in the direction of the Small Magellatic Cloud and the limits of an extragalactic soft X-ray flux

Previously reported X-ray data from the vicinity of the Small Magellanic Cloud (SMC) have been reanalyzed using H I data from a more detailed and sensitive 21-cm survey of this region. The results support the previous conclusion: assuming that the interstellar material absorbs according to the cross sections of Brown and Gould (1970), at least 75 per cent of the observed 0.25-keV X-ray flux is of local origin. The corollary problem of placing a cosmologically useful upper limit on the extragalactic flux will be difficult to solve until the behavior of the local component is better understood; but if the local flux is isotropic, a 3-sigma upper limit of 240 photons per (sq cm s sr keV) at 0.25 keV may be placed on a flux originating beyond the SMC. Tables of H I column density are given for an area 30 deg by 30 deg about the SMC. The high-velocity component, presumably associated with the Magellanic Cloud system, and the galactic disk component are tabulated separately.

Mccammon, D.↗
NASA NTRS1975

Aluminum under high pressure. I - Equation of state

A curve of applied pressure versus lattice constant is calculated for single-crystal aluminum. It results from an application of the method of structural expansions for deriving the energies of simple metals, a method known to give reasonable results for the elastic constants even at second order in the effective electron-ion interaction. The latter is taken from Fermi-surface analysis, and it is verified that the extant face-centered cubic structure remains the preferred crystalline phase up to the highest pressures considered. Arguments are given to suggest that the curve should have reasonable a priori accuracy and can admit possible improvement if experimental data in the intermediate-pressure region can be provided to refine the (in principle) energy-dependent pseudopotential. At three megabars, the lattice constant is reduced by only 22 per cent; the ion cores at this pressure are still very well separated.

Friedli, C.↗
NASA NTRS1976

Aioun el Atrouss - A new hypersthene achondrite with eucritic inclusions

Preliminary investigations have been made on two separate pieces from the Aioun el Atrouss meteorite that fell on April 17, 1974 in southeast Mauritania. The major portion of the meteorite is a brecciated hypersthene achondrite with orthopyroxene (En74) as the major phase. Clasts of eucrite, up to 7 per cent in volume within a single slice, occur within the hypersthene achondrite host. No evidence has been found of reaction between the two meteorite types, nor of the presence of any materials intermediate in composition.

Lomena, I. S. M.↗
NASA NTRS1977

Gravitational potential energy of the earth: A spherical harmonic approach

A spherical harmonic equation for the gravitational potential energy of the earth is derived for an arbitrary density distribution by conceptually bringing in mass-elements from infinity and building up the earth shell upon spherical shell. The zeroth degree term in the spherical harmonic equation agrees with the usual expression for the energy of a radial density distribution. The second degree terms give a maximum nonhydrostatic energy in the mantle and crust of -2.77 x 10 to the twenty-ninth power ergs, an order of magnitude. If the earth is assumed to be a homogeneous viscous oblate spheroid relaxing to an equilibrium shape, then a lower limit to the mantle viscosity of 1.3 x 10 to the twentieth power poises is found by assuming the total geothermal flux is due to viscous dissipation. If the nonequilibrium figure is dynamically maintained by the earth acting as a heat engine at one per cent efficiency, then the viscosity is ten to the twenty second power poises, a number preferred by some as the viscosity of the mantle.

Rubincam, D. P.↗
NASA NTRS1977

A computer program for the identification of helicopter impulsive noise sources

A computer program is presented for calculating the source location of implusive noise in helicopters. The program (INSL) is written in FORTRAN for the CDC 7600 computer. Inputs are the rotor operating conditions and the time intervals (T) between rotor 1/rev index and impulsive noises as measured by different microphones. The outputs are the possible noise source locations in terms of rotor radial and azimuthal coordinates. Typical computer time for a run of six microphone measurements is 1.5 sec, and the cost is about 12 cents for the CDC 7600.

Lee, A.↗
NASA NTRS1976

Evaluation of Landsat image registration accuracy

The Large Area Crop Inventory Experiment (LACIE) is an attempt to demonstrate the capability to forecast the annual production of major crops such as wheat and corn. Good image registration of data acquired on different dates is one of the key assumptions made in LACIE. This paper describes an algorithm to measure the accuracy of the current registration procedure. This algorithm employs a modified version of sequential similarity detection algorithm (SSDA). Based on over 264 registration checks, it was found that the root-mean-square of registration errors was 1.0 pixel. The failure rate of our registration checking algorithm was less than 10 per cent and the standard deviation of the accuracy of this algorithm was less than 0.2 picture element.

Kaneko, T.↗
NASA NTRS1976

The effective temperature of Uranus

Uranus was observed in the spectral region from 40 to 250 microns with a 102-cm balloon-borne telescope, and the results were interpreted in terms of model atmosphere calculations to yield an effective temperature of 58 plus or minus 3 K; this sets an upper limit of about 28 per cent on the relative contribution of an internal heat source to the total thermal radiation. On the same flight, the brightness temperatures of Venus (215 plus or minus 13 K) and Jupiter (135 plus or minus 6 K) were also measured, thus reconfirming the existence of an internal heat source for Jupiter.

Fazio, G. G.↗
NASA NTRS1976

Near-uv photon efficiency in a TiO2 electrode - Application to hydrogen production from solar energy

An n-type (001) TiO2 electrode irradiated at 365 nm was tested under anodic polarization. A saturation current independent of pH and proportional to light intensity has been observed. Accurate measurements of the incident power lead to a 60 per cent photon efficiency. A photoelectrochemical cell built with such an electrode, operated under solar irradiation without concentration, produced an electrolysis current of 0.7 mA/sq cm without applied voltage.

Desplat, J.-L.↗
NASA NTRS1976

Monitoring complex trace-gas mixtures by long-path laser absorption spectrometry

Laser-based spectrophotometric methods, which have been proposed for the detection of trace concentrations of gaseous contaminants, include Raman and passive radiometry. The paper discusses a simple long-path laser absorption method which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels. A number of species were selected which are most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Absorption coefficients at CO2 laser wavelengths were measured, accurate to + 3 per cent or better, for each of these species. This data base was then used to determine the presence and concentration of the contaminants in prepared mixtures of 12 to 15 gases. Computer programs have been developed which will permit a real-time analysis of the monitored atmosphere. Minimum detectable concentrations for individual species are generally in the ppm range, and are not seriously degraded by interferences even in complex mixtures. Estimates of the dynamic range of this monitoring technique for various system configurations and comparison with other methods of analysis are discussed

Green, B. D.↗
NASA NTRS1977

Gas-rich minerals in the Allende meteorite - Attempted chemical characterization

A ten-step etching experiment with HNO3 was performed on a chromite-carbon residue from Allende, in order to characterize the HNO3-soluble minor phase 'Q' that contains most of the primordial Ar, Kr, and Xe. Each etch fraction was analyzed by neutron activation analysis for Cr, Fe, Co, Ir, and Au. The results suggest that Q consists of two minerals, each comprising about 5 per cent of the residue. Phase Q1, of Fe/Cr ratio greater than 20, is soluble in cold dilute HNO3 and seems to contain most of the heavy noble gases. It may be an HCl-insoluble sulfide of nominal composition (Fe84Ni12Cr4)Sx. Phase Q2, of Fe/Cr ratio about 0.5 and somewhat enriched in Co, is slowly soluble in hot concentrated HNO3 and seems to be at least an order of magnitude poorer in heavy noble gases than Q1. It may be daubre-elite or an acid-soluble variety of chromite.

Gros, J.↗
NASA NTRS1977

A contribution to computer analysis of coupled-cavity traveling wave tubes

A flexible accurate large-signal computer program has been developed for the design of coupled-cavity traveling wave tubes. The program is written for a TSS-360 time sharing system. The beam is described by a disk model and the slow wave structure by a sequence of cavities or cells. The computational approach is arranged so that each cavity may have different geometrical or electrical parameters than its neighbors. This allows the program user to simulate a tube of almost arbitrary complexity. Input and output couplers, severs, complicated velocity tapers, and other features peculiar to one or a few cavities may be modeled by a correct choice of input data. The beam-wave interaction is handled by a new approach in which the RF fields are expanded in solutions to the TM wave equation retaining all significant space harmonics. The program was used to perform a design study of the TWT developed for the CTS satellite. Good agreement was obtained between the predictions of the program and the measured performance of the flight tube. The internal check on power balance was satisfied within plus or minus 0.2 per cent of input beam power.

Connolly, D. J.↗
NASA NTRS1977

Effect of vegetation on rock and soil type discrimination

The effect of naturally occurring vegetation on the spectral reflectance of earth materials in the wavelength region of 0.45 to 2.4 microns is determined by computer averaging of in situ acquired spectral data. The amount and type of vegetation and the spectral reflectance of the ground are considered. Low albedo materials may be altered beyond recognition with only ten per cent green vegetation cover. Dead or dry vegetation does not greatly alter the shape of the spectral reflectance curve and only changes the albedo with minimum wavelength dependency. With increasing amounts of vegetation the Landsat MSS band ratios 4/6, 4/7, 5/6, and 5/7 are significantly decreased whereas MSS ratios 4/5 and 6/7 remain entirely constant.

Siegal, B. S.↗
NASA NTRS1976

Status of silicon solar cell technology

It is pointed out that during the time from 1970 to 1976 the efficiency of solar cells has increased from 10.5 to 15.5%. Most of the increased output has resulted from increased short circuit current. Advances leading to this improvement in performance are discussed, taking into account a reduction in the area covered by the grid pattern, the use of antireflection coatings, and the employment of surface texturizing. A widespread use of solar cells for nonspace applications requires a reduction in the cost of solar cell arrays from the present $20 per watt to 10 to 50 cents per watt. Approaches for achieving this objective are considered. Attention is given to an automated, high volume production of solar cells made from ribbon silicon or thin film layers.

Brandhorst, H. W., Jr.↗