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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Operating limitations of high speed jet lubricated ball bearings

A parametric study was performed with 120-mm bore angular-contact ball bearings having a nominal contact angle of 20 degrees. The bearings had either an inner- or an outer-race land riding cage, and lubrication was by recirculating oil jets which had either a single or dual orifice. Thrust load, speed, and lubricant flow rate were varied. Test results were compared with those previously reported and obtained from bearings of the same design which were under-race lubricated but run under the same conditions. Jet lubricated ball bearings were limited to speeds less than 2,500,000 DN, and bearings having inner-race land riding cages produced lower temperatures than bearings with outer-race land riding cages. For a given lubricant flow rate dual orifice jets produced lower bearing temperatures than single orifice jets, but under-race lubrication produced lower bearing temperatures under all conditions of operation with no apparent bearing speed limitation.

Zaretsky, E. V.↗
NASA NTRS1975

Combustor exhaust-emissions and blowout-limits with diesel number 2 and jet A fuels utilizing air-atomizing and pressure atomizing nozzles

Experimental tests with diesel number 2 and Jet A fuels were conducted in a combustor segment to obtain comparative data on exhaust emissions and blowout limits. An air-atomizing nozzle was used to inject the fuels. Tests were also made with diesel number 2 fuel using a pressure-atomizing nozzle to determine the effectiveness of the air-atomizing nozzle in reducing exhaust emissions. Test conditions included fuel-air ratios of 0.008 to 0.018, inlet-air total pressures and temperatures of 41 to 203 newtons per square centimeter and 477 to 811 K, respectively, and a reference velocity of 21.3 meters per second. Smoke number and unburned hydrocarbons were twice as high with diesel number 2 as with Jet A fuel. This was attributed to diesel number 2 having a higher concentration of aromatics and lower volatility than Jet A fuel. Oxides of nitrogen, carbon monoxide, and blowout limits were approximately the same for the two fuels. The air-atomizing nozzle, as compared with the pressure-atomizing nozzle, reduced oxides-of-nitrogen by 20 percent, smoke number by 30 percent, carbon monoxide by 70 percent, and unburned hydrocarbons by 50 percent when used with diesel number 2 fuel.

Ingebo, R. D.↗
NASA NTRS1974

A novel negative-limited sealed nickel-cadmium cell

The use of negative-limited nickel-cadmium cells with adequate charge control is shown to provide an effective means for controlling internal pressure. Cycle test data show that negative-limited cells have somewhat higher ampere-hour degradation rates at higher operating temperatures. The most important advantages of these cells are: (1) lesser heat generation during operation; (2) longer separator life, as a result of operation at lower temperatures; (3) decreased stresses on cell seals due to lower operating pressures; and (4) significant weight savings.

Juvinall, G. L.↗
NASA NTRS1974

An upper limit to the product of NO and O densities from 105 to 120 km

From the Ogo 6 horizon-scanning-photometer data a useful upper limit can be set to the radiance of nightglow in the O-NO afterglow continuum above 105 km. The upper limit is a factor of about 5 less than the product of observed NO densities and Jacchia (1971) O model densities.

Donahue, T. M.↗
NASA NTRS1974

Limit pulses in passive nonlinear absorbers

The propagation of coherent pulses in absorbers with nonlinear refractive index is investigated. It is shown that a term neglected by previous authors places an upper limit on the attainable field strength in steady-state pulses. In ruby with a Cr(3+) doping density of 10 to the 17th power per cu cm, for example, this limit is less than 2,000,000 V/cm.

Lee, C. T.↗
NASA NTRS1975

Upper limits of hard gamma-ray emission from six X-ray sources

The Cornell 100-inch gamma-ray telescope has been used to set upper limits for the gamma-ray flux above 400 MeV from the X-ray sources Cyg X-1, Cyg X-2, Cyg X-3, Cas A, Cas B, and Per X-1. An upper limit for the diffuse flux of the galactic disk was set which is consistent with OSO-3 and SAS-2 data. A new measurement of the atmospheric gamma-ray generation rate is presented.

Campbell, M.↗
NASA NTRS1975

Upper mass limits for stable rotating white dwarfs

Models of nonmagnetic axisymmetric differentially rotating zero-temperature white dwarfs are constructed and tested for stability. Upper mass limits, beyond which models become secularly and dynamically unstable to growth of nonaxisymmetric perturbations, are found at 2.5 solar masses and 4.6 solar masses, respectively. The upper mass limit for secular stability is practically the same for the two angular momentum distributions considered. Crude growth rates due to gravitational radiation and degenerate-electron viscosity are calculated for the secularly unstable models. Except for a narrow parameter range, gravitational radiation is the dominant destabilizing mechanism. For masses between 3.5 and 4.6 solar masses, the secular instability grows on a time scale of about 10 to 1000 years; for masses exceeding about 4.6 solar masses, the dynamic instability grows on a time scale of seconds. Implications of these results for mass-transfer binary star systems and degenerate stellar cores are discussed.

Durisen, R. H.↗
NASA NTRS1975

Upper limits for X-ray emission from Jupiter as measured from the Copernicus satellite

X-ray telescopic observations are made by the Copernicus satellite for detecting X-ray emission from Jupiter analogous to X-rays from terrestrial aurorae. Values of X-ray fluxes recorded by three Copernicus detectors covering the 0.6 to 7.5 keV energy range are reported. The detectors employed are described and the times at which the observations were made are given. Resulting upper-limit spectra are compared with previous X-ray observations of Jupiter. The upper-limit X-ray fluxes are discussed in terms of magnetospheric activity on Jupiter.

Vesecky, J. F.↗
NASA NTRS1974

Theoretical frameworks for testing relativistic gravity. 5: Post-Newtonian limit of Rosen's theory

The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the PPN parameter alpha sub 2, which is related to the difference in propagation speeds for gravitational and electromagnetic waves. Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific but presumably special form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity--and standard solar system experiments cannot distinguish between the two theories.

Lee, D. L.↗
NASA NTRS1976

Automatic noise limiter-blanker

A blanker system that may be used with audio noise limiters or automatic noise limiters was described. The system employs a pair of silicon diodes and two RC filters connected across the feedback impedance of an operational amplifier so as to counteract impulse noise interference caused by local spherics activity or 60 Hz harmonics radiated from ac motor control systems. The following information is given: circuit diagram and description, operating details, evaluation, discussion of other noise blanking methods.

Burhans, R. W.↗
NASA NTRS1976

No new limit on the size distribution of gamma-ray bursts

The results of a study (Carter et. al.) of gamma ray bursts using long duration balloon exposure are analyzed. Arguments are presented against the conclusion that the size spectrum extrapolates to a power law with index from -1.0 to -0.5, and that therefore the gamma ray bursts are of galactic origin. It is claimed that the data are consistent with an upper limit over 100 times that proposed, and that therefore no conclusion can be drawn from the measurements regarding the nature or origin of gamma ray bursts. The resulting upper limit to the rate of occurrence of small bursts lies above the -1.5 index power law extrapolation of the size spectrum of known events, i.e., greater than the rate expected from an infinitely extended source region.

Cline, T. L.↗
NASA NTRS1975

Operating limitations of high-speed jet-lubricated ball bearings

A parametric study was performed with 120-mm bore angular-contact ball bearings having a nominal contact angle of 20 deg. The bearings either had an inner- or an outer-race land riding cage. Lubrication was by recirculating oil jets. The oil jets either had a single or dual orifice. Thrust load, speed, and lubricant flow rate were varied. Test results were compared with those previously reported and obtained from bearings of the same design which were under-race lubricated but run under the same conditions. Jet lubricated ball bearings were limited to speeds less than 2,500,000 DN. Bearings having inner-race land riding cages produced lower temperatures than bearings with outer-race land riding cages. For a given lubricant flow rate dual orifice jets produced lower bearing temperatures than single orifice jets. However, under-race lubrication produced under all conditions of operation lower bearing temperatures with no apparent bearing speed limitation.

Zaretsky, E. V.↗
NASA NTRS1976

Limit on the secular change of the gravitational constant based on studies of solar evolution

The past and present observable properties of the sun have been theoretically calculated on the assumption that the gravitational constant G increases or decreases with time. Consideration of Davis's experimental upper limit on the present solar neutrino flux and of terrestrial paleontological data sets a limit on the absolute rate of change of G, namely, the absolute value of the quotient of the change in the gravitational constant and the gravitational constant is less than 1/10 billion/yr, if other standard constants do not also change with time.

Chin, C.-W.↗
NASA NTRS1976

New upper limits for atmospheric constituents on Io

A spectrum of Io from 0.86 to 2.7 microns with a resolution of 3.36 per cm and a signal to rms noise ratio of 120 is presented. No absorptions due to any atmospheric constituents on Io could be found in the spectrum. Upper limits of 0.12 cm-atm for NH3, 0.12 cm-atm for CH4, 0.4 cm-atm for N2O, and 24 cm-atm for H2S were determined. Laboratory spectra of ammonia frosts as a function of temperature were compared with the spectrum of Io and showed this frost not to be present at the surface of Io. A search for possible resonance lines of carbon, silicon, and sulfur, as well as the 1.08-micron line of helium, proved negative. Upper emission limits of 60, 18, 27, and 60 kilorayleighs, respectively, were established for these lines.

Fink, U.↗
NASA NTRS1976

Theoretical frameworks for testing relativistic gravity. V - Post-Newtonian limit of Rosen's theory

The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the post-Newtonian parameter alpha sub 2 (which is related to the difference in propagation speeds for gravitational and electromagnetic waves). Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific (but presumably special) form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity - and standard solar system experiments cannot distinguish between the two theories.

Lee, D. L.↗
NASA NTRS1976

Basic limits on protocol information in data communications networks

The paper considers basic limitations on the amount of protocol information that must be transmitted in a data communication network to keep track of source and receiver addresses and of the starting and stopping of messages. Assuming Poisson message arrivals between each communicating source-receiver pair, a lower bound is found on the required protocol information for message. This lower bound is the sum of two terms, one for the message-length information, which depends only on the distribution of message lengths, and the other for the message-start information, which depends only on the product of the source-receiver pair arrival rate and the expected delay for transmitting the message. Two strategies are developed which, in the limit of large numbers of sources and receivers, almost meet the lower bound on protocol information.

Gallager, R. G.↗
NASA NTRS1976

A new luminosity limit for spherical accretion onto compact X-ray sources

Preheating of infalling gas by emergent X-rays can suppress accretion on to a compact X-ray source. For spherically symmetric accretion, the effect results in a new luminosity limit, orders of magnitude less than the Eddington limit, above which steady flow is impossible. The model may apply to the globular-cluster X-ray sources.

Ostriker, J. P.↗