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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Interaction of rotor tip flow irregularities with stator vanes as a noise source

The role of the interaction of rotor tip flow irregularities (vortices and velocity defects) with downstream stator vanes is discussed as a possible fan noise mechanism. This is accomplished by: (1) indicating some of the mothods of formation of these flow irregularities; (2) observing how they would behave with respect to known noise behavior; and (3) attempting to compare the strength of the rotor tip flow irregularity mechanism with the strength of the more common rotor wake-stator mechanism. The rotor tip flow irregularity-stator interaction is indicated as being a probable inflight noise source.

Dittmar, J. H.↗
NASA NTRS1977

Regenerable device for scrubbing breathable air of CO2 and moisture without special heat exchanger equipment

The device concerns the circulation of cabin air through canisters which absorb and adsorb carbon dioxide, together with excess moisture, and return the scrubbed air to the cabin for recirculation. A coating on an inert substrate in granular form absorbs and adsorbs the impurities at standard temperatures and pressures, but desorbs such impurities at low pressures (vacuum) and standard temperatures. This fact is exploited by making the device in a stack of cells consisting of layers or cells which are isolated from one another flow-wise and are connected to separate manifolds and valving systems into two separate subsets. A first subset may be connected for the flow breathable air therethrough until the polyethyleneimine of its cells is saturated with CO2 and H2O. During the same period the second subset of cells is manifolded to a vacuum source.

Tepper, E. H.↗
NASA NTRS1977

Spectral characteristics of 3U 1915-05, a burst source candidate

An X-ray burst source has been discovered near the X-ray source 3U 1915-05. The continuum spectra of both the burst source and the quiescent source 3U 1915-05 are hard, with kT for thermal bremsstrahlung models above 20 keV. The spectrum of 3U 1915-05 has a feature at 9.1 keV, which, if attributed to absorption by hydrogen and heliumlike iron, suggests the presence of a highly ionized cloud surrounding a central X-ray source.

Becker, R. H.↗
NASA NTRS1977

Interaction of rotor tip flow irregularities with stator vanes as a noise source

The role of the interaction of rotor tip flow irregularities (vortices and velocity defects) with downstream stator vanes is discussed as a possible fan noise mechanism. This is accomplished by: indicating some of the methods of formation of these flow irregularities; observing how they would behave with respect to known noise behavior and; attempting to compare the strength of the rotor tip flow irregularity mechanism with the strength of the more common rotor wake-stator mechanism. The rotor tip flow irregularity-stator interaction is indicated as being a probable inflight noise source.

Dittmar, J. H.↗
NASA NTRS1978

Pattern recognition methods and air pollution source identification

Directional air samplers, used for resolving suspended particulate matter on the basis of time and wind direction were used to assess the feasibility of characterizing and identifying emission source types in urban multisource environments. Filters were evaluated for 16 elements and X-ray fluorescence methods yielded elemental concentrations for direction, day, and the interaction of direction and day. Large numbers of samples are necessary to compensate for large day-to-day variations caused by wind perturbations and/or source changes.

Leibecki, H. F.↗
NASA NTRS1979

The MIT/OSO 7 catalog of X-ray sources - Intensities, spectra, and long-term variability

This paper is a summary of the observations of the cosmic X-ray sky performed by the MIT 1-40-keV X-ray detectors on OSO 7 between October 1971 and May 1973. Specifically, mean intensities or upper limits of all third Uhuru or OSO 7 cataloged sources (185 sources) in the 3-10-keV range are computed. For those sources for which a statistically significant (greater than 20) intensity was found in the 3-10-keV band (138 sources), further intensity determinations were made in the 1-15-keV, 1-6-keV, and 15-40-keV energy bands. Graphs and other simple techniques are provided to aid the user in converting the observed counting rates to convenient units and in determining spectral parameters. Long-term light curves (counting rates in one or more energy bands as a function of time) are plotted for 86 of the brighter sources.

Markert, T. H.↗
NASA NTRS1980

The X-ray superbubble in Cygnus

It is shown that Cyg X-6 and Cyg X-7 are part of a large X-ray ring, 13 degrees in diameter. At a distance of 2 kpc, this X-ray source lies behind the Great Rift of Cygnus, and as such has radiation from its central region absorbed. The diameter of the emitting region is 450 pc. The X-ray source is associated with a ring of elongated H-alpha filaments which enclose the Cygnus X radio source. At the center of this region lies the highly luminous Cygnus OB2 association.

Cash, W.↗
NASA NTRS1984

A theoretical model for the cross spectra between pressure and temperature downstream of a combustor

A theoretical model developed to calculate pressure-temperature cross spectra, pressure spectra, temperature spectra and pressure cross spectra in a ducted combustion system is presented. The model assumes the presence of a fluctuating-volumetric-heat-release-rate disk source and takes into account the spatial distribution of the steady-state volumetric-heat flux. Using the model, pressure, velocity, and temperature perturbation relationships can be obtained. The theoretical results show that, at a given air mass flow rate, the calculated pressure-temperature cross spectra phase angle at the combustor exit depends on the model selected for the steady-state volumetric-heat flux in the combustor. Using measurements of the phase angle, an appropriate source region model was selected. The model calculations are compared with the data. The comparison shows good agreement and indicates that with the use of this model the pressure-temperature cross spectra measurements provide useful information on the physical mechanisms active at the combustion noise source.

Miles, J. H.↗
NASA NTRS1984

Variability of the ultraviolet spectrum of BL Lacertae objects

Attention is given to repeated observations of the two nearby BL Lac objects, Mrk 421 and PKS 0521-36, comparing the temporal behavior of their continuum in the 1300-3000 A range with that observed in intrinsically bright BL Lac objects and in Seyfert galaxies. Also discussed are the emission lines in the UV and optical spectrum of PKS 0521-36. It is suggested that the difference in variability pattern between BL Lac objects and Seyfert galaxies may be due to differences in the properties of the nonthermal continuum related to differences in accretion regimes, although it is more probably due to the presence of different continuum components in Seyfert galaxies. In BL Lac objects, the UV spectrum is likely to be synchrotron radiation from an optically thin source.

Ulrich, M. H.↗
NASA NTRS1983

X-ray observations of Crab-like supernova remnants

Distinguishing radio and morphological characteristics of Crab Nebula-like supernova remnants (SNR) are described. Radio features comprise a flat spectrum, a filled center brightness distribution, and a centrally located pulsar. The radio signals are linearly polarized and suggest a synchrotron emission mechanism. Known objects with those characteristics include the Crab Nebula, Vela X, 3C58, G21.5 - 0.9 and G74.9 + 1.2. Only the Crab Nebula exhibits pulsations, while all have unresolved X-ray sources and nonthermal X-ray spectra. Although the Crab-like SNR are distinctly different from shell-like SNR, the SNR CTB80, G326.3 - 1.8, W28 and G29.7 0.3 display characteristics of both, particularly shell-like structures and flat spectra. X-ray spectra from compact sources have also been detected from 3C58, CTB80, W28 and MSH 15 - 52 and exhibit nonthermal power law features. The X-ray spectra could be used as a measure of the evolutionary stage of the source.

Becker, R. H.↗
NASA NTRS1985

Considerations for upgrading modifications to the Marshall Space Flight Center's X-ray calibration facility

The Marshall Space Flight Center's X-ray Calibration Facility was constructed for preflight calibration of the HEAO-B X-ray Telescope (1978-1981). Calibration requirements for a newly proposed X-ray telescope, AXAF (scheduled for flight early 1990's), go beyond the capabilities of the facility at present. Several of these new requirements are discussed, among them: (1) the production of a pure unpolarized X-ray beam, (2) minimizing the target/tube change over time, and (3) how to configure the X-ray source chamber to effectively accommodate both polarized and unpolarized X-ray sources.

Kitterman, J. H.↗
NASA NTRS1986

WAMDII observation of an auroral atmosphere wave event

Field tests of WAMDII (Wide Angle Michelson Doppler Imaging Interferometer) on February 23 to 24, 1984 in Saskatoon produced wind images of the aurora that show well defined wave structures in lambda 5577. Wavelengths and velocities of these structures suggest an acoustic-gravity wave interpretation, but their short duration warrants their being termed an event. The Dopplergrams are presented with emphasis on the interpretation of the waves and a discussion of possible sources.

Wiens, R. H.↗
NASA NTRS1985

Radio and X-ray observations of G11.2 - 0.3 and G41.1 - 0.3

The supernova remnants G11.2 - 0.3 and G41.1 - 0.3 have been observed in radio and X-ray utilizing the VLA and Einstein Observatory, respectively. The acquired images reveal that both sources have shell morphologies and do not exhibit any clear indication of a central stellar remnant. In addition, both objects are relatively bright X-ray sources.

Becker, R. H.↗
NASA NTRS1986

Active control of propeller induced noise fields inside a flexible cylinder

An active noise control model has been evaluated for reducing aircraft interior noise. The structural noise transmission properties of an aircraft fuselage were modelled as a flexible cylinder excited by external acoustic dipoles simulating the noise produced by twin propellers. The amplitudes of an internal distribution of monopole control sources were determined such that the area-weighted mean square acoustic pressure was minimized in the propeller plane. The noise control model was evaluated at low frequencies corresponding to the blade passage frequency and first few harmonics of a typical turbo-prop aircraft. Interior noise reductions of 20 25 dB were achieved, over a substantial region of the cylindrical cross-section, with just a few monopole control sources. The most favorable interior noise reductions were achieved when the active noise control model was used in combination with propeller source phasing.

Lester, H. C.↗
NASA NTRS1989

Solar wind control of Jupiter's hectometric radio emission

Radio, plasma, and magnetic field data obtained by Voyager 1 and Voyager 2 were used to examine the manner in which the Jovian hectometric radio emission (HOM) is controlled by the solar wind. Using the method of superposed epochs, it was found that the higher energy HOM is correlated with the IMF as well as with the solar wind density and pressure. However, unlike the Io-independent decametric radio emission (Non-Io DAM), the HOM displayed no correlation with the solar wind velocity, although this radio component appear to be also influenced by the IMF. The results suggest separate HOM amd Non-Io DAM sources.

Barrow, C. H.↗
NASA NTRS1989

A complete sample of double-lobed radio quasars for VLBI tests of source models - Definition and statistics

A complete, flux-density-limited sample of double-lobed radio quasars is defined, with nuclei bright enough to be mapped with the Mark III VLBI system. It is shown that the statistics of linear size, nuclear strength, and curvature are consistent with the assumption of random source orientations and simple relativistic beaming in the nuclei. However, these statistics are also consistent with the effects of interaction between the beams and the surrounding medium. The distribution of jet velocities in the nuclei, as measured with VLBI, will provide a powerful test of physical theories of extragalactic radio sources.

Hough, D. H.↗
NASA NTRS1989

Unsteady disturbances of streaming motions around bodies

The present investigation of flows around bodies with a stagnation point notes that the vortical part of such flows becomes singular along the entire body surface and its wake; as a result, the potential part of the flow will also be singular along the entire surface. A modified splitting of the velocity field is proposed which encompasses: (1) a vortical part having zero streamwise and normal components along the body surface; (2) an entropy-dependent part; and (3) a regular part similar to the potential part which satisfies a linear inhomogeneous wave equation with a modified source term.

Atassi, H. M.↗
NASA NTRS1989

Instrumental and atmospheric background lines observed by the SMM gamma-ray spectrometer

Preliminary identifications of instrumental and atmospheric background lines detected by the gamma-ray spectrometer on NASA's Solar Maximum Mission satellite (SMM) are presented. The long-term and stable operation of this experiment has provided data of high quality for use in this analysis. Methods are described for identifying radioactive isotopes which use their different decay times. Temporal evolution of the features are revealed by spectral comparisons, subtractions, and fits. An understanding of these temporal variations has enabled the data to be used for detecting celestial gamma-ray sources.

Share, G. H.↗