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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 37 records · Page 2
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NASA NTRS1974

Stress analysis of the compact specimen including the effects of pin loading

An improved method of boundary collocation was applied to the two-dimensional stress analysis of the compact specimen. The effects of the pin-loaded holes on stress-intensity factors and crack-opening displacements were investigated for various crack-length-to-specimen-width ratios, hole locations, and internal loadings. The stress-intensity factors for the 'standard' compact specimen under plane-stress or plane-strain conditions were found to be within 1 percent of the stress-intensity factors reported in the ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-72) over a range of crack-length-to-specimen-width ratios of 0.4 to 0.7. However, for crack-length-to-specimen-width ratios less than 0.4, the pin-load holes (which were not previously accounted for) had a significant effect on stress intensity and crack-opening displacements.

Newman, J. C., Jr.↗
NASA NTRS1975

Compaction by impact of unconsolidated lunar fines

An investigation was conducted concerning the macroscopic irreversible partial compaction of terrestrial or lunar fines. A sample material (70051), assumed to be typical of the fines in the unconsolidated material of the lunar regolith, was used in the experiments. Tests were also carried out with powdered Vacaville basalt. Release adiabate and Hugoniot measurements were conducted. It was found that the dynamic stresses required for irreversible compaction of lunar fines on the moon are significantly lower than the values inferred from the shock recovery experiments conducted by Christie et al. (1973).

Ahrens, T. J.↗
NASA NTRS1976

Radio continuum measurements of compact H II regions and other sources

Results are reported for measurements of the flux densities of 33 sources at wavelengths of 13, 4, and 2 cm, which were conducted using the NASA/JPL Deep Space Network 64-m antenna at Goldstone, Calif. Besides compact H II regions, the sources included five Uhuru X-ray sources, several IR sources, an extragalactic radio source, and a H2O maser. The Lyman continuum flux is derived from the measured radio flux and the assumed distance and temperature for 10 possible H II regions; the spectra of previously known sources are extended to higher frequencies, and upper limits are placed on the flux densities for the five X-ray sources. New compact H II regions are found in the bright nebula M78, the nebula K5, and the Ophiuchus dark cloud/IR region.

Matsakis, D. N.↗
NASA NTRS1976

Optical, infrared and radio studies of compact H II regions. I - The complex in S 106

The paper reports on combined optical, infrared, and radio observations of the compact complex S 106. The source could be resolved into ten components, three of which are compact components of size approximately 0.2 pc and were detected at 12.6 microns and 2.7 GHz. Two of the components are point-like sources detected at 8000 A. One of the components detected at 8000 A is spatially coincident with a strong 3.5 micron source and is suggested as a possible exciting star for the complex.

Pipher, J. L.↗
NASA NTRS1975

On the problems associated with the rapidly varying compact nonthermal sources

Difficulties and possible interpretations are discussed for observations of extragalactic compact nonthermal radio sources. The sources considered are those which have been identified optically with normal and peculiar galaxies, quasars, N galaxies, and BL Lacertae objects. Optical, infrared, and radio flux variations in different sources are noted along with difficulties associated with determining angular sizes from interferometric measurements. It is suggested that the ultimate origin of the infrared flux is probably a nonthermal synchrotron mechanism in some sources and absorption and reradiation of ultraviolet synchrotron radiation by dust in others. Model calculations of compact sources are reviewed, emphasizing equipartition of energy, total energies, the importance of the Compton effect, and sources which present severe difficulties for the theory of a canonical incoherent electron-synchrotron source.

Burbidge, G. R.↗
NASA NTRS1977

A compact radio source in the nucleus of M82

The brightest compact radio source in the nucleus of M82 has a linear diameter of about 0.02 parsecs (25 light-days). On the basis of this small size and energy considerations, it seems that this source is probably not a supernova remnant, but is similar in nature to the compact radio sources found in the nuclei of spiral and elliptical galaxies, Seyfert galaxies, radio galaxies, and in quasi-stellar objects.

Geldzahler, B. J.↗
NASA NTRS1977

An angular size for the compact radio source at the galactic center

Simultaneous very-long-baseline (100 million wavelengths) and intermediate-baseline (4 million wavelengths) interferometer observations at a wavelength of 3.7 cm in 1976.2 show that the galactic-center compact radio source has a linear size of approximately 140 AU. The observations also set an upper limit of about 0.1 Jy to the emission from any core of size less than roughly 10 AU at that epoch. The total flux density of the compact source was slightly higher than the value reported previously.

Lo, K. Y.↗
NASA NTRS1978

X-ray and radio emission from the compact galaxy III Zw 2

X-rays from the compact galaxy III Zw 2 have been detected with the rotating modulation collimator on board SAS 3. The (2-10-keV) flux is (4.3 + or - 0.5) by 10 to the -11th power erg/sq cm per sec, which corresponds to a luminosity of 1.4 by 10 to the 45th power erg/s at 530 Mpc. Subsequent radio observations between 1.46 and 90 GHz were made at the NRAO Very Large Array and 36-foot (11-m) installations. The radio spectrum rises sharply toward higher frequencies and, below about 100 GHz, is indicative of a self-absorbed synchrotron spectrum from an extremely compact, rapidly evolving object.

Schnopper, H. W.↗
NASA NTRS1978

Relativistic blast-wave model for the rapid flux variations of AO 0235+164 and other compact radio sources

A relativistic blast-wave version of a signal-screen model is developed which can adequately explain the details of the flux-density and structural variations of compact extragalactic radio sources. The relativistic motion implied by flux variations is analyzed with respect to the synchrotron spectrum of the BL Lac object AO 0235+164 observed during outbursts, and a signal-screen model for rapidly expanding shells produced by ultrarelativistic blast waves is examined. The approximate observed structure of the blast wave at three stages in its evolution is illustrated, each stage is described, and the model is applied to the flux density outburst in AO 0235+164 observed in late 1975. The results show that a relativistic blast-wave model can in general reproduce the main features of the observed flux variations in compact sources. Some problems with the proposed model are briefly discussed.

Marscher, A. P.↗
NASA NTRS1979

Mode 1 crack surface displacements for a round compact specimen subject to a couple and force

Mode I displacement coefficients along the crack surface are presented for a radially cracked round compact specimen, treated as a plane elastostatic problem, subjected to two types of loading; a uniform tensile stress and a nominal bending stress distribution across the net section. By superposition the resultant displacement coefficient or the corresponding influence coefficient can be obtained for any practical load location. Load line displacements are presented for A/D ratios ranging from 0.40 to 0.95, where A is the crack length measured from the crack mouth to the crack tip and D is the specimen diameter. Through a linear extrapolation procedure crack mouth displacements are also obtained. Experimental evidence shows that the results are valid over the range of A/D ratios analyzed for a practical pin loaded round compact specimen.

Gross, B.↗
NASA NTRS1978

The central, compact source in the Cygnus A galaxy

Single, optically thin, component models as well as double, optically thick at low frequencies, component models have been examined in trying to explain the central source in the nucleus of Cygnus A. In the course of exploring those models, it is found that this compact radio source may be quite similar to other compact and variable sources in Seyfert galaxies and quasars. Double component models generally do better because they fit the X-rays, and there is a good chance that the X-rays arise in the central source; these models can naturally explain variability which may already have been detected in X-rays. The IR is most likely due to emission by cold dust in the nucleus of Cygnus A. Optical emission is, very likely, primarily thermal, except perhaps at UV wavelengths. A number of observations are suggested to check the predictions of this work.

Kafatos, M.↗
NASA NTRS1979

Absorption models for low-frequency variability in compact radio sources

The consequences of the most plausible version of the absorption model for low-frequency variability in compact extragalactic radio sources are considered. The general restrictions placed on such a model are determined, and observational tests are suggested that can be used either to support the model or to discriminate among its various versions. It is shown that low-frequency variability in compact radio sources can be successfully explained by a class of models in which the flux is modulated by changes in free-free optical depth within an intervening ionized medium. Two versions of such a model are distinguished, one involving large changes in optical depth and the other, small changes. It is noted that while absorption effects are capable of causing rapid flux and structural variations at centimetric wavelengths, the models predict detailed behavior that is in direct conflict with observational data.

Marscher, A. P.↗
NASA NTRS1979

Compact H II regions in the far-infrared

Far-infrared (40-150 microns) observations of W51 (G49.5-0.4), K3-50, DR 21, NGC 7538, and W3(OH) are presented and discussed. At these wavelengths each source is dominated by a small bright component closely associated with a compact H II region. Their spectra can be explained as emission by dust at temperatures of 30-50 K. Some of the objects appear to be optically thick out to wavelengths of about 60 microns. Of the 10 source components in the five regions, at least four may be powered by pre-main-sequence stars. The far-infrared data are consistent with depletion of volatile components of the dust within compact H II regions, but do not clearly require destruction or expulsion of refractory grains. The bulk of the dust which emits primarily in the far-infrared must lie in a dense shell immediately outside the ionized zone. The sources are possible precursers to open clusters with stellar masses in the range from 1,000 to 10,000 solar masses.

Thronson, H. A., Jr.↗
NASA NTRS1979

Mode I crack surface displacements for a round compact specimen subject to a couple and force

Mode I displacement coefficients along the crack surface are presented for a radially cracked round compact specimen, treated as a plane elastostatic problem, subjected to two types of loading; a uniform tensile stress and a nominal bending stress distribution across the net section. By superposition the resultant displacement coefficient or the corresponding influence coefficient can be obtained for any practical load location. Load line displacements are presented for A/D ratios ranging from 0.40 to 0.95, where A is the crack length measured from the crack mouth to the crack tip and D is the specimen diameter. Through a linear extrapolation procedure crack mouth displacements are also obtained. Experimental evidence shows that the results of this study are valid over the range of A/D ratios analyzed for a practical pin loaded round compact specimen.

Gross, B.↗
NASA NTRS1980

Spectroscopy of compact extragalactic X-ray sources

The X-ray spectra of compact extragalactic sources obtained from the HEAO-1 A-2 experiment and the solid-state spectrometer onboard HEAO-2 (the Einstein Observatory) are reviewed. Seyfert spectra are remarkably consistent with characteristic power-law spectra of energy index alpha = 0.7 + .1 over a dynamic range of almost 100 in both luminosity for the whole sample, and energy for individual members. Radio-quiet quasars have similar spectra, perhaps slightly steeper, for the limited sample available. New solid-state spectrometer results for NGC 4151 yield a consistent picture for the geometry of the broad-line clouds in both these related radio-quiet classes of galactic nuclei. Radio-loud objects, especially BL Lacs, are considerably more variable in spectrum as well as luminosity. Direct synchrotron and synchrotron-self-Compton components are consistent with what we observe from these objects. Finally, the role of spectroscopy in addressing the extent to which compact extragalactic nuclei might contribute to the diffuse X-ray background is discussed.

Holt, S. S.↗
NASA NTRS1979

Theories of magnetospheres around accreting compact objects

The paper reviews theoretical models of magnetospheres formed around neutron stars and other strongly magnetized compact objects in the presence of mass accretion from a companion star. Emphasis is placed on the interaction of the accretion process with the magnetic field of the compact object and the formation of a magnetosphere. The following models are discussed: magnetospheres with polar funnels; closed magnetospheres and their instabilities; models of internal flow; and disk accretion magnetospheres.

Vasyliunas, V. M.↗
NASA NTRS1980

A collection of formulas for calculation of rotating blade noise - Compact and noncompact source results

A unified approach is used to derive many of the current formulations for calculation of discrete frequency noise for helicopter rotors and propellers. Both compact and noncompact source formulations are derived. The compact formulations are obtained as the limit of noncompact source results. In particular, the linearized acoustic equations by Hawkings and Lowson, Farassat, Hanson, Woan and Gregorek, Succi, and Jou are derived in this paper. An interesting thickness noise formula by Isom and its recent extension to the near field by Ffowcs Williams are also presented. The paper includes some comparisons of measured and calculated acoustic pressure signatures and spectra for an advanced propeller. The theoretical results are obtained using a computer program developed by the author and P. A. Nystrom.

Farassat, F.↗