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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 469 records · Page 26
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NASA NTRS1983

A note on compressibility and energy cascade in turbulent molecular clouds

Observed velocity-size correlations are reexamined in the light of an improved theory of turbulent energy cascade that is developed. It is shown that observed velocity-size correlations cannot be compared with the Kolmogorov law, which is based on incompressible turbulent flow. The fact that the log v-log(l/rho) scaling law (v the turbulent velocity, l the associated region size, and rho the fluid density) predicted for compressible energy cascade is always steeper than that observed in molecular clouds indicates the injection rather than the dissipation of mechanical energy at smaller scales of motion. It is also shown that the concept of strict energy cascade may not be generally applicable in the interstellar medium. The agreement between theory and observation turns out to be best for small cool clouds and cloud cores, suggesting that, for these regions at least, the dominant process in establishing the observed v-l-rho correlation is a turbulent energy cascade.

Fleck, R. C., Jr.↗
NASA NTRS1982

JBFA - buoyant flight

A method was developed whereby a balloon was used to carry lumber out of a forest in order to continue lumber production without destroying the natural environment and view of the forest. Emphasis was on the best shape for a logging balloon, development of a balloon logging system suitable for cutting lumber and safety plans, tests on balloon construction and development of netting, and weather of mountainous areas, especially solutions to problems caused by winds.

Ohari, T.↗
NASA NTRS1983

Gamma Ray Bursts: a 1983 Overview

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect; energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all; burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective; finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T. L.↗
NASA NTRS1983

Einstein X-ray observations of optical-radio selected areas

Einstein Observatory Imaging Proportional Counter X-ray observations of fields in SA 57, SA 68, and U Mi that possess deep optical and radio coverage have been conducted with a sensitivity comparable to that of the Einstein Observatory's medium sensitivity survey of serendipitous X-ray sources. The number of X-ray sources detected is consistent with a log N(greater than S) - log S slope of about -1.5. The fraction of active galactic nuclei in the X-ray sample is less than about 50 percent, with the rest being composed of clusters and normal galaxies, consistent with the medium sensitivity survey.

Katgert, P.↗
NASA NTRS1984

A comparative review of radiation aerosol models

Aerosol characteristics to be introduced into a set of models within a framework of a Standard Radiation Atmosphere (SRA) are reviewed, and a reconciliation of the Toon and Pollack (TP) global model with the SRA models is attempted. Among the topics discussed are physical and radiative characteristics, radiation aerosol models, albedo for single scattering, and phase function and spectral variation of extinction. Size distribution models are also covered, inclusive the Junge power law, and the modified gamma-, log normal-, and zold-distribution. Recommendations include modifying the SRA profile VI to resemble the Elterman profile modified in the TP model, improving discontinuity at the tropopause level for all SRA models, and retaining the same log-normal size distribution for all SRA components.

Lenoble, J.↗
NASA NTRS1984

Compositional trends and cooling rates of group IVB iron meteorites

It is found, on the basis of new neutron activation data for group IVB, that log-element - log-Ni trends are best understood in terms of core formation and fractional crytstallizaion. The limited compositional range found in gorup IVB is thought to reflect the fact that, owing to the low concentrations of S, P, and C and the high concentration of Ni, the k sub x (the solid/liquid partition ratio) values are closer to unity than are those in other magmatic groups. Mean volatile abundances in group IVB are significantly lower than those found in any group of chondritic meteorites, indicating that these low abundances are not entirely the result of nebular processes and that planetary outgassing was also involved.

Rasmussen, K. L.↗
NASA NTRS1984

Chemical and physical studies of type 3 chondrites. III Chondrules from the Dhajala H3.8 chondrite

Thermoluminescence (TL) properties have been measured in 58 chondrules separated from the Dhajala H3.8 chondrite. The pyrolytic chondrules are noted to have higher mass-normalized TL values than nonpyrolytic ones. Significant correlations are noted between log(TL) and the bulk CaO, Al2O3, and MnO content of the chondrules. These, together with correlations of log(TL) with the CaO, Al2O3, SiO2 and normative anorthite content of the chondrule glass, indicate an association of the TL and the abundance and position of mesostasis. It is suggested that the TL level in a given chondrule is governed by its bulk composition and metamorphism, and it is hypothesized that the devitrification resistance of unequilibrated chondrule mesostasis explains the unequilibration of certain chondrules in type 3 ordinary chondrites.

Sears, D. W. G.↗
NASA NTRS1984

IUE spectroscopy of the degenerate components in the Hyades close binaries V471 Tauri and HZ9

Effective temperatures and gravities have been determined for the degenerate components in the Hyades close binaries V471 Tauri and HZ9 from model atmosphere analysis of IUE ultraviolet spectra. For V471 Tauri, T(e) = 35,000 K and log g is about 8. For HZ9, T(e) = 20,000 K and log g = 8. Both systems contain DA2 white dwarfs. No photospheric metal lines were detected at low IUE resolution in either DA2 star. The 1400 A and 1600 A features are absent in the HZ9 degenerate, despsite being within the temperature range of some other DA stars with the 1400 A absorption feature.

Guinan, E. F.↗
NASA NTRS1984

Classical free-streamline flow over a polygonal obstacle

In classical Kirchhoff flow, an ideal incompressible fluid flows past an obstacle and around a motionless wake bounded by free streamlines. Since 1869 it has been known that in principle, the two-dimensional Kirchhoff flow over a polygonal obstacle can be determined by constructing a conformal map onto a polygon in the log-hodograph plane. In practice, however, this idea has rarely been put to use except for very simple obstacles, because the conformal mapping problem has been too difficult. This paper presents a practical method for computing flows over arbitrary polygonal obstacles to high accuracy in a few seconds of computer time. We achieve this high speed and flexibility by working with a modified Schwarz-Christoffel integral that maps onto the flow region directly rather than onto the log-hodograph polygon. This integral and its associated parameter problem are treated numerically by methods developed earlier by Trefethen for standard Schwarz-Christoffel maps.

Elcrat, A. R.↗
NASA NTRS1985

Preparations of methoxynitrophenazines and their photoconductivities

Eight methoxynitrophenazines with a methoxy group at the 1 or 2 position and a nitro group at the 6-, 7-, 8- or 9-position of the phenazine ring 1,6, 1,7. 1,8, 1,9, 2,6, 2,7, 2,8 and 2,9 were prepared and their photocurrents were measured by illuminating the surface-type cell with white light from a W lamp under a N atmosphere at room temp. The photocurrents of 1-nitrophenazine 6 and 2-nitrophenazine 7 are compared with those of the methoxynitrophenazines. The photocurrent (i sub p) increases with increasing light intensity (I), thus satisfying log i varies as n log I. The n values are 0.5-1.0. When the nitro group is located at the beta-position of the phenazine ring, the photocurrent becomes larger owing to the electron withdrawing property of the nitro group. On the other hand, the photocurrents of phenazines with the nitro group at the Alpha-position are extremely small. The photoconductivities of methoxynitrophenazines are lower in air.

Sugimoto, A.↗
NASA NTRS1984

High resolution evidence for the Garrett-Munk spectrum of stratospheric gravity waves

Vertical profiles of scalar horizontal winds have been measured at high resolution (10 m) in the 13 to 37 km region of the stratosphere. This resolution (at that range of altitude) represents the state-of-the-art, and is unique. The technique used smoke trails laid by rockets in the stratosphere, and were taken by AFGL at Wallops Island, VA, White Sands Missile Range, NM, and Ft. Churchill, Canada, in the 1977-78 time period. Two or three cameras were used to give the time-lapse photographs. The goal was to ascertain whether or not the internal waves of the stratosphere behave consistently with the Garrett-Munk model which was originally created for oceanic internal waves. Five profiles of horizontal wind are presented. It is concluded: (1) stratospheric internal waves obey the Garrett-Munk model for vertical wave numbers; (2) there is not statistically significant evidence for a break in the curve at high wave numbers when due allowance is made for aliasing effects; and (3) the power density level of the spectra are almost equal on a log-log scale in spite of the difference in time, season, and geographical location.

Dewan, E. M.↗
NASA NTRS1985

Adiabatic thermal models for planetary bodies

In a number of recent experiments it was found that the logarithmic derivative with respect to volume of the adiabatic temperature increase with pressure P to be an approximately constant quantity n. It was found that n decreases slightly with temperature, to be virtually unaffected by increasing pressure and to take values between 4 and 8 for a wide variety of materials. It is shown that these findings can be substantiated from thermodynamic arguments, finite strain theory, atomic potential theory and experimental data on the thermal expansion coefficient and the bulk modulus B. It will be shown that n is independent of pressure if it is exactly equal to dB/dP + 1. For these materials d log gamma/d log v = -1, where gamma is the thermodynamic Gruneisenparameter. It will increase with P during an isothermal transformation if n dB/dP + 1 and decrease of n dB/dP + 1. For most materials n is close to dB/dP and the changes will be slight if pressures do not become too extreme. During an adiabatic transformation n is virtually constant. Adiabatic thermal models for planetary bodies were calculated and are presented.

Spohn, T.↗
NASA NTRS1985

Measurement and correlation of jet fuel viscosities at low temperatures

Apparatus and procedures were developed to measure jet fuel viscosity for eight current and future jet fuels at temperatures from ambient to near -60 C by shear viscometry. Viscosity data showed good reproducibility even at temperatures a few degrees below the measured freezing point. The viscosity-temperature relationship could be correlated by two linear segments when plotted as a standard log-log type representation (ASTM D 341). At high temperatures, the viscosity-temperature slope is low. At low temperatures, where wax precipitation is significant, the slope is higher. The breakpoint between temperature regions is the filter flow temperature, a fuel characteristic approximated by the freezing point. A generalization of the representation for the eight experimental fuels provided a predictive correlation for low-temperature viscosity, considered sufficiently accurate for many design or performance calculations.

Schruben, D. L.↗
NASA NTRS1985

The method for the study of the inelastic cross-section for high energy protons by means of shower arrays with the large calorimetric area

Proton initiated showers could be reliably separated from showers initiated by cosmic ray nuclei by means of arrays with large calorimetric area, using distributions of energy fractions for EAS electromagnetic muon and hadron components. Proton initiated showers penetrate deeper into the atmosphere and have relatively lower energy fraction in muons. Distribution of that energy fraction is sensitive to the value of the proton inelastic cross-section. It is shown that the analysis of this distribution let one distinguish between log sup 2 S -rise and log S -rise of the cross-section at energies above 10 to the 15th power eV.

Danilova, T. V.↗
NASA NTRS1984

On the surface density of X-ray selected BL Lacertae objects

Only a handful of BL Lac objects have been found as a result of systematic optical identification of serendipitous Einstein X-ray sources. By combining the data from two flux-limited complete X-ray surveys (the HEAO 1 A-2 and the Einstein Observatory Medium Sensitivity Survey) the surface density of X-ray emitting BL Lac objects is evaluated as a function of their X-ray flux. It is found that a single power law is not an acceptable representation of the BL Lac objects' X-ray log N-log S. The number-flux relationship is consistent with the Euclidean slope at 'high' flux levels but shows a drastic flattnring below fluxes of the order of 10 to the -12th ergs per sq cm/s. The implications of this result are briefly discussed with respect to the luminosity function, the cosmological evolution, and the X-ray to optical flux ratio in BL Lac objects.

Maccacaro, T.↗
NASA NTRS1984

The CN radical in diffuse interstellar clouds

A survey of 15 lines of sight for the CN B2Sigma(+) X2Sigma(+) interstellar absorption lines shows that the CN column density in diffuse interstellar clouds follows the relation log N(CN) is proportional to m log N(H2), where m is approximately equal to 3. This result is reproduced by a reaction network in which CN is produced primarily from C2 by the neutral-neutral reaction C2 + N yields CN + C, and photodissociation is the main destruction pathway for the neutral molecules CH, C2, and CN. The CN radical is the first molecular species observed in diffuse clouds that requires a neutral-neutral reaction for its formation in the gas phase. The network also reproduces the observed ratio N(CN)/N(H2).

Federman, S. R.↗
NASA NTRS1985

The frequency of weak gamma-ray bursts

A search for weak gamma-ray bursts was conducted using a sensitive balloon-borne detector. One burst was detected in 64 hr of observation. The upper limit to the burst rate is 2300 bursts/yr above 6 x 10 to the -7th ergs/sq cm for simple spatial distribution models. Comparison with satellite results indicates that the slope of the log N-log S curve can be no steeper than -1 between 10 to the -4th and 10 to the -6th ergs/sq cm. A detailed procedure for calculating detector sensitivity to bursts is provided.

Meegan, C. A.↗
NASA NTRS1985

Characterization of X-ray sources detected in a deep Einstein exposure of the field around 3C 295

An extensive set of optical and radio observations is presented that characterize the X-ray sources detected in an extremely deep Einstein Observatory exposure of the 3C 295 region. A total of five X-ray sources was found. This number is consistent with the only previous log N - log S result published at these flux levels. One of the sources was a galactic star. The four extragalactic sources are active galactic nuclei (three Seyferts and one QSO). Two of the sources are Seyfert galaxies in the 3C 295 cluster, one of which was previously unknown. The number of Seyfert galaxies in the cluster that is found from this complete X-ray survey is inconsistent with that expected from the fraction of low-redshift active galactic nuclei in their clusters.

Henry, J. P.↗