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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The Tidbinbilla-U.K. Schmidt radio quasar identification program

A program is under way at Tidbinbilla to measure accurate (up to 2 arcsec r.m.s) radio positions for compact sources in the Parkes 2.7 GHz survey south of declination -30 deg. Optical identifications are being made on the basis of radio-optical position coincidence alone, without regard to colour or morphology, using the U.K. Schmidt IIIa-J sky survey to a limiting magnitude of 22.5. This program is aimed at producing an evaluation of the radio quasar redshift distribution with particular emphasis on those objects with redshifts greater than 3.0.

Jauncey, D. L.↗
NASA NTRS1984

Non-enzymatic template-directed synthesis on RNA random copolymers - Poly(C, U) templates

Random copolymer templates containing cytosine and uracil in ratios of 3:1 and 1:1 are used to explore the optimum conditions for efficient synthesis of guanine and adenine-containing oligonucleotides. The experimental procedure is described, including the preparation of mononucleoside 5'-phospho-2-methylimidazolides and random copolymers, the template-directed oligomerization, the removal and reintroduction of mononucleotides in interrupted reactions, the determination of oligomerization efficiency, the alkaline and enzymatic hydrolysis of reaction products, and the column chromatography. Results are presented and discussed for the dependence of adenine incorporation on the formation of short oligo(G)s, optimization of incorporation efficiencies by adjusting monomer concentrations, the characterization of oligomeric product distribution, and the regiospecificity of adenine incorporation. The prebiotic significance of the results is assessed.

Joyce, G. F.↗
NASA NTRS1987

An L-U implicit multigrid algorithm for the three-dimensional Euler equations

An LU implicit multigrid scheme is developed for the calculation of three-dimensional transonic flow through rotating cascades. This numerical method solves the unsteady Euler equations of gas dynamics in a finite-volume form. The implicit scheme makes it possible to take a much larger time step than is normally permitted in most explicit schemes, while the multigrid method is incorporated to accelerate the convergence rate for steady state calculations. Using this method, computational storage requirements are comparable to those of explicit schemes, while operation counts are considerably less than those found in the more widely-used ADI schemes.

Yokota, Jeffrey W.↗
NASA NTRS1988

U-Pb ages and Sr, Pb and Nd isotope data for gneisses near the Kolar Schist Belt: Evidence for the juxtaposition of discrete Archean terranes

Uranium-lead ages and Sr, Pb, and Nd isotopic data for gneisses near the Kolar Schist Belt and their interpretation as evidence for the juxtaposition of discrete Archean terranes were presented. The granodioritic Kambha gneiss east of the schist belt has a zircon age of 2532 + or - 3 Ma and mantle-like initial Sr, Pb, and Nd isotopic ratios. Therefore these gneisses are thought to represent new crust added to the craton in the latest Archean. By contrast, more mafic Dod gneisses and leucocratic Dosa gneisses west of the schist belt (2632 + or - 7 and 2610 + or - 10 Ma) show evidence for contamination of their magmatic precursors (LREE-enriched mantle-derived for the Dod gneisses) by older (greater than 3.2 Ga) continental crust. Fragments of this older crust may be present as granitic and tonalitic inclusions in the 2.6-Ga gneisses and in shear zones. The antiquity of these fragments is supported by their Nd, Sr, and Pb isotopic compositions and by 2.8 to greater than 3.2 Ga zircon cores.

Krogstad, E. J.↗
NASA NTRS1989

U. radio emission from quiescent filaments

Full-disk Very Large Array (VLA) synthesis maps of the quiet Sun indicate that filaments can be seen in emission at 91.6 cm wavelength; they are detected in absorption at shorter microwave wavelengths. The 91.6 cm emission has a brightness temperature of T sub B = 3 x 10(exp 5) K. It is hotter, wider and longer than the underlying filament detected at H alpha wavelengths, but the similarity between the shape, position, elongation and orientation of the radio and optical features suggests their close association. The 91.6 cm emission is attributed to the thermal-bremsstrahlung of a hot transition sheath that envelopes the H alpha filament and acts as an interface between the cool, dense H alpha filament and the hotter, rarefied corona. The transition sheath is seen in emission because of the lower optical depth of the corona at 90 cm wavelength, and the width of this sheet is 10(exp 9) cm. A power law gradient in pressure provides a better match to the observations than a constant pressure model; definitive tests of theoretical models await simultaneous multi-wavelength studies of filaments at different observing angles. When the thermal bremsstrahlung is optically thin, the magnetic field strength in the transition sheath can be inferred from the observed circular polarization. Variable physical parameters of the sheath, such as width, electron density, and electron temperature, can explain controversial reports of the detection of, or the failure to detect, the meter-wavelength counterpart of H alpha filaments.

Lang, Kenneth R.↗
NASA NTRS1990

Tropical Rainfall Measuring Mission (TRMM) project. III - Japan-U.S. collaborative rain observation experiment using an airborne rain radar

A collaborative rain-observation experiment using an airborne rain radar was conducted between Communications Research Laboratory (CRL) and Goddard Space Flight Center (GSFC)/NASA. CRL provided an airborne rain-radar/radiometer system and GSFC/NASA provided a NASA P3-A aircraft. Airborne or spaceborne rain-radar echoes have large sea or land-surface echoes. These surface echoes yield rain-estimation algorithms using rain attenuation. The experiment demonstrated the potential of the rain-estimation techniques using rain attenuation.

Meneghini, Robert↗
NASA NTRS1992

Observation and interpretation of the asymmetric Stokes Q, U, and V line profiles in sunspots

We present a first approach to systematic characterization and interpretation of observed asymmetries of Stokes profiles as a function of spatial position within sunspots. Spatial maps of the full Stokes profiles of Fe I 6302.5 A gathered in large sunspots using the HAO Stokes II instrument reveal asymmetries that vary systematically across large sunspots observed during 1980. We use the inversion technique by Landolfi to extract the velocity gradients along the line of sight (LOS) which give rise to these asymmetries. The gradients derived from full Stokes profiles are in agreement with previous characterizations of the Evershed flow derived from Stokes I profiles alone (i.e., a flow increasing with depth in the atmosphere). By coupling this semiempirical gradient of velocity with a magnetic field inclination varying along the LOS, the synthesized profiles are able to mimic basic observed features of the broad-band circular polarization present in our data and observed previously by others. This characterization has magnetic field lines which become progressively more horizontal with depth in the penumbra.

Sanchez Almeida, J.↗
NASA NTRS1993

Comment on 'The semiannual variation of great geomagnetic storms and the postshock Russell-McPherron effect preceding coronal mass ejecta' by N. U. Crooker, E. W. Cliver and B. T. Tsurutani

It is proposed by Crooker et al. (1992) that for a subgroup of great geomagnetic storms, for which the associated strong southward IMF (B(S)) fields reside in the postshock plasma, preceding the driver gas of coronal mass ejections, such strong B(S) fields result from a 'major increase in the Russell-McPherron polarity effect, through a systematic pattern of compression and draping' of the Archimedean field in the x-y plane. The critics test the scenario proposed by Crooker et al., namely, that the Russell-McPherron polarity effect is a major contribution to the semiannual variable of intense geomagnetic storms. It is found by the critics that in the cases studied there is little difference between the B(S) values as measured in geocentric solar ecliptic and geocentric solar magnetospheric coordinates, and it is concluded that the Russell-McPherron mechanism cannot explain by itself the seasonal dependence of intense storms, for which the variation is the largest. Crooker et al. present arguments to show that the combined preshock and postshock Russell-McPherron effect remains the sole cause of the semiannual variation of great storm occurrence.

Gonzalez, W. D.↗
NASA NTRS1993

Th-230 - U-238 series disequilibrium of the Olkaria basalts Gregory Rift Valley, Kenya: Petrogenesis

Strong mixing trends on a (Th-230/Th-232) versus Th diagram show that the basalts are mixed magmas which have undergone interaction with the crust. Instantaneous Th/U ratios are less than time integrated ones but these exceed the Th/U ratios in the MORB and OIB sources. This indicates that the mantle may have undergone some metasomatic fluxing, crustal contamination of the basalts will also enhance these ratios. Early activity on the Akira plain is represented by early basalts and hawaiites. The early basalt samples are known to predate the earliest comendites. The most recent phase of activity is represented by another cinder cone 40-50 m high being feldspar and clinopyroxene phyric. Inclusions which occur in the comendites vary in size and distribution. The largest and most porphyritic are the trachytes (up to 40 cm) with alkali feldspar phases up to 6 mm and small pyroxenes in the ground mass. The second set of inclusions are smaller (up to 10 cm) and are largely aphyric. The distribution of the inclusions are not uniform, the Broad Acres (C5) lavas contain 2-5 percent. The size of the inclusions decrease from south to north, as does the abundance of the trachytic inclusions. The major element variations in the Naivasha basalts, hawaiites and magmatic inclusions are discussed.

Black, S.↗
NASA NTRS1993

The Th and U abundances in chondritic meteorites

We present new analyses of Th-232/U-238 in CI and CM meteorites. The relative abundance of these nuclides is important in estimates of the age of r-process elements. The cosmochronology based upon the Th-232/U-238 ratio (kappa) depends on the precise determinations of these two different elements in meteorites and on the production ratios. Both parameters are subject to substantial errors. Recent recalculations of this chronology have used selected values from compilations but do not adequately address the errors in terms of a reliable data base. Morgan and Lovering provided extensive neutron activation analyses for ordinary chondrites which yield an average kappa of 3.6 +/- 0.4. Their work on carbonaceous chondrites showed a wide range in kappa from 2 to 6. More recent investigations by isotopic dilution have established the following: (1) highly variable kappa from 2.7 to 11 in Allende Ca-Al-rich inclusions and a value of 3.6 in the Orgueil CI1 chondrite; (2) a range from 2.71 to 6.63 for 7 L-type chondrites and a range from 2.7 to 4.4 for 6 L, H, and LL chondrites. A further investigation of this subject matter is presented.

Chen, J. H.↗
NASA NTRS1961

Some Nuclear Calculations of U-235-D2O Gaseous-Core Cavity Reactors

The results of a multigroup, diffusion theory study of spherical gaseous-core cavity reactors are presented in this report. The reactor cavity of gaseous U235 is enclosed by a region of hydrogen gas and is separated from an external D2O moderator-reflector by a zirconium structural shell. Some cylindrical reactors are also investigated. A parametric study of spherical reactors indicates that, for the range of variables studied, critical mass increases as: (1) Fuel region is compressed within the reactor cavity, (2) moderator thickness is decreased, (3) structural shell thickness is increased, and (4) moderator temperature is increased. A buckling analogy is used to estimate the critical mass of fully reflected cylindrical reactors from spherical results without fuel compression. For a reactor cavity of a 120-centimeter radius uniformly filled with fuel, no structural shell, a moderator temperature of 70 F, and a moderator thickness of 100 centimeters, the critical mass of a spherical reactor is 3.1 kilograms while that of a cylinder with a length-to-diameter ratio of 1.0 (L/D = 1) is approximately 3.8 kilograms and, with L/D = 2, 5.9 kilograms. For the range of variables considered for U235-D2O gaseous-core cavity reactors, the systems are characterized by 95 to 99 percent thermal absorptions, with the flux reaching a maximum in the moderator about 10 to 15 centimeters from the reactor cavity.

Ragsdale, Robert G.↗