SEARCH · Search NASA

Results for “source strength”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22

All sources NASA NTRS DOE OSTI

NASA NTRS1974

Temperature compensated digital inertial sensor

A circuit which maintains the inertial element of a gyroscope or accelerometer at a constant position by delivering pulses to a rebalancing motor is discussed. The circuit compensates for temperature changes by using a temperature sensor that varies the threshold of inertial element movement required to generate a rebalance pulse which reacts to changes in viscosity of the flotation fluid. The output of the temperature sensor also varies the output level of the current source to compensate for changes in the strength of the magnets of the rebalancing motor. The sensor also provides a small signal to the rebalance motor to provide a temperature dependent compensation for fixed drift or fixed bias.

Hand, P. J.↗

NASA NTRS1974

Episodic release of Ar-40 from the interior of the moon

Measurements of lunar atmosphere made by the mass spectrometer at the Apollo 17 landing site during the first 9 lunations of 1973 show an apparently cyclical variation of radiogenic Ar-40, with maximum to minimum abundance ratio of about 2. There seems to be a 6-7 month periodicity in the oscillation, but the limited data base makes a fixed oscillatory pattern uncertain. The significance of the variation of atmospheric argon lies in the implication that its source is episodic in nature, ranging in strength from about 1% of the total rate of production of Ar-40 in the moon to near zero. This requires a presently active mechanism for transient venting of gas from deep within the moon.

Hodges, R. R., Jr.↗

NASA NTRS1985

Explosive Welding for Remote Applications

Explosive seam welding produces up to 100-percent joint strength. Ribbon explosive activated by remote energy source produces metallurgically sound joint. Success of technique verified for joints between like metals and joints between two different metals. Applications include structural assembly in toxic atmospheres and in radioactive or otherwise hazardous environments.

Bement, L. J.↗

NASA NTRS1988

Gravitational wave searches using the DSN (Deep Space Network)

The Deep Space Network Doppler spacecraft link is currently the only method available for broadband gravitational wave searches in the 0.01 to 0.001 Hz frequency range. The DSN's role in the worldwide search for gravitational waves is described by first summarizing from the literature current theoretical estimates of gravitational wave strengths and time scales from various astrophysical sources. Current and future detection schemes for ground based and space based detectors are then discussed. Past, present, and future planned or proposed gravitational wave experiments using DSN Doppler tracking are described. Lastly, some major technical challenges to improve gravitational wave sensitivities using the DSN are discussed.

Nelson, S. J.↗

NASA NTRS1993

Energy distributions of radio galaxies

Far-infrared observations of 140 radio galaxies which span a range of over four orders of magnitude in radio power, (from weak nuclear sources in nearby galaxies, to powerful FR II doubled lobed sources at moderate redshift) are presented. The strength of the far-infrared emission is more closely correlated with core than total radio emission. Far-infrared emission in radio galaxies represents star formation that is more closely tied to the active nucleus than to the global properties of the galaxy. The far-infrared luminosity function shows good continuity between radio galaxies and radio loud quasars.

Impey, Chris↗

NASA NTRS1994

Regulation of assimilate partitioning by daylength and spectral quality

The effects of daylength and spectral quality on assimilate partitioning and leaf carbohydrate content should be considered when conducting controlled environment experiments or comparing results between studies obtained under different lighting conditions. Changes in partitioning may indicate alterations to photoregulatory processes within the source leaf rather than disruptions in sink strength. Moreover, it may be possible to use photoregulatory responses of assimilate partitioning to probe mechanisms of growth and development involving translocation of carbon or adaptation to environmental factors such as elevated CO2. It may also be possible to steer assimilate partitioning for the benefit of controlled environment agriculture using energy-efficient manipulations such as daylength extensions with dim irradiances, end-of-day alterations in light quality, or shifting plants between different spectral qualities as a part of phasic control of growth and development. Note that high starch levels measured on a one-time basis provide little information, since it is the proportion of photosynthate stored as starch that is meaningful. Large differences in starch content can result from small changes in partitioning integrated over several days. Rate information is required.

Britz, Steve J.↗

NASA NTRS1986

Application of a relativistic jet model to the study of BL Lacertae objects

The development of a relativistic jet model and its use in fitting coordinated observations of the BL Lacertae objects Mrk 180, Mrk 421, and Mrk 501 are described. This model is a modified version of one by Koenigl (1981). The present model fits show that the properties of the jets in all three objects are similar. The variation in the angle between the jet axis and the observer's line of sight accounts for the differing degrees of variability of the sources. For the case where the jet is seen close to the line of sight (Mrk 421), the Doppler enhanced nonthermal radiation dominates the optical flux. The variation of particle density and magnetic field strength along the jets is similar in all three sources, and suggests that the energy flux is dominated by the magnetic field in the inner regions and by the particle energy at large distances from the jet apex. This result is consistent with models of jets in which the Poynting flux drives particle acceleration at large jet radii.

Hutter, D. J.↗

NASA NTRS1992

Evidence for an ionized reprocessor in NGC 6814

A detailed spectroscopic analysis of a Ginga observation of the Seyfert galaxy NGC 6814 is reported. It is shown that the X-ray data are consistent with a scenario in which the continuum radiation is reprocessed in a highly ionized medium, which can either be an accretion disk or a shell of absorbing material. Both of these can produce the strong observed iron K-alpha line, which must originate within 200 lt-sec of the continuum source. Significant iron K-beta and nickel K-alpha are predicted, based on the iron K-alpha line strength, and these lines partially conceal the iron edge in this source. The spectral variability below about 4 keV, where the apparent absorption increases as the continuum flux decreases, is probably caused by a warm absorber covering the reprocessing system.

Turner, T. J.↗

NASA NTRS1994

Energetic ion distributions on both sides of the Earth's magnetopause

The Active Magnetospheric Particle Tracer Explorer/Charge Composition Explorer (AMPTE/CCE) spacecraft, with an apogee of approximately 8.8R(sub E) and an inclination of approximately 4.3 deg, sampled the outer dayside equatorial magnetosphere for extended time periods and often crossed into the magnetosheath whenever the solar wind pressure was sufficiently high to compress the magnetopause to less than 8.8R(sub E). We have analyzed ion distributions on both sides of the magnetopause in order to investigate any local time and energy dependence, giving information about physical processes at the magnetopause and the bow shock. Particle measurements are from the Charge Energy Mass (CHEM)(1.5 to 300 keV/e) and Medium-Energy Particle Analyzer (MEPA)(10 keV to 2 MeV) instruments. The wide total energy range (1.5 keV to 2 MeV) covered describes the magnetospheric distributions quite well, and for the purpose of this study, adequately describes the high-energy part of the shocked solar wind. Thus both solar wind and magnetospheric components can be recognized in a mixed particle distribution. Case studies of representative magnetopause crossings at dawn, noon, and dusk, as well as a survey of several other crossings, indicated: (1) a local time and energy dependence of magnetosheath spectra at energies greater than or equal to 50 KeV; spectra were harder at the duskside than at the dawnside and also correlated with magnetospheric activity, (2) constantly much higher intensities in the magnetosphere than in the magnetosheath at energies greater than 10 KeV and an earthward gradient in the subsolar magnetosheath. In addition to the steady state magnetosheath population there exists a burst-type component indicative of a magnetospheric source, and most of the time this is recognized as a flux transfer event. Overall, the results about the origin of the greater than or equal to 50 KeV magnetosheath ions are consistent with the continuous leakage of magnetospheric particles across a tangential discontinuity magnetopause, locally distributed according to magnetospheric drift paths. Magnetic reconnection, although present, should not be a dominant source on average, because it is not continuous in time. Fermi acceleration should not be dominant because it predicts the opposite local time asymmetry, and shock drift acceleration should be a minor contributor at E greater than or equal to 50 keV because of upper-energy cutoff limitations. Our observations also indicate a significant magnetospheric contribution to energies as low as approximately 10 KeV, where the magnetosphere-magnetosheath intensity gradient reverses. However, in orderto examine the relative strength and local time distribution of all possible sources at these energies, a detailed analysis is required.

Paschalidis, N. P↗

NASA NTRSDate not supplied

Impact Experiments into Granular Targets Containing Solitary Blocks of Varying Strength and Size

Crater scaling relationships provide a means to correlate dimensions of laboratory-scale impact experiments to naturally formed craters at planetary scales. For relatively larger impact events, where gravity is the dominant arresting force against crater growth, these scaling relations are comparatively simple. For smaller craters, however, the target properties have increasing influence over the cratering process. Further complexities are easily envisaged when considering realistic surfaces that contain small-scale heterogeneities in cohesive strength, density, porosity, friction, as these properties will each have unequal effects on the resultant crater morphometry. Even when produced under controlled laboratory conditions, understanding (and controlling) the entire relevant parameter space is daunting, and deconvolution of the relevant contributors can be complicated even in the best-case scenario. To this end, we have begun an extensive series of impact experiments that will provide a nascent framework that will aid in the interpretation of craters observed on complex natural surfaces throughout the solar system. To start with the simplest configuration, experiments were performed with cylindrical PVC buckets that were filled with quartz sand and contained a single cubic block of synthetic sandstone. The blocks varied in size (14-33 mm) and unconfined compressive strength (0.5-7.4 MPa) and were placed in/on the sand along the trajectory of the incoming impactor and buried to different depths. All experiments were conducted using the vertical gun located in the Experimental Impact Lab at NASA Johnson Space Center with alumina projectiles that were accelerated to ~1.53 km s^-1 under a vacuum of 1 torr. After the impact, target containers were removed from the chamber are morphometric data were extracted by using a Peel 2 3D-scanner in combination with the open-source software, CloudCompare. Initial results show that block strength is a secondary effect on crater diameter and depth, but when at least one edge of the block is exposed and the surface (partial burial) the strength will dictate the number of surviving block fragments around the crater, as well as how much disrupted block material is retained within the crater walls.

Christopher J. Cline II↗

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 NTRS1979

New method for determining relative oscillator strengths of atoms through combined absorption and emission measurements - Application to titanium /Ti I/

The paper introduces a procedure that combines measurements of absorption and emission by atoms to obtain relative oscillator strengths that are independent of temperature determination in the sources and of assumptions regarding local thermodynamic equilibrium. The experimental observations are formed into sets of transitions and required to satisfy defined ratios. The procedure is illustrated with the published data of Whaling et al. and Smith and Kuehne for 16 transitions in Ti I. It is shown that the relative oscillator strengths resulting from this procedure have calculated uncertainties between 5 and 17% (about 95% confidence level). Evidence is presented to suggest that these uncertainties have been overestimated.

Cardon, B. L.↗

NASA NTRS2025

Source-Time Dominant Modeling of the Doppler Shift for the Auralization of Moving Sources

When developing an auralization for acoustic scenarios involving moving sources and receivers, one key feature is the ability to simulate the Doppler shift, i.e., the changing frequency content from the receiver’s perspective. As the time-varying delay between a source and receiver is what accounts for the Doppler shift, an approximation of this delay is required to successfully render the changes in frequency content at the receiver. Depending on the signal-processing strategy chosen to accomplish this task, there is, how-ever, a potential to introduce audible artifacts due to frequency folding (aliasing), frequency replication (imaging), and broadband noise. In this paper we dis-cuss the manifestation of such artifacts and propose a method to eliminate them, which can be integrated into the digital signal processing chain of larger auralization schemes. The method is built upon a source-time dominant approach and uses a combination of oversampling, interpolation, and time-varying filtering to predict and eliminate frequency regions at the receiver that are vulnerable to aliasing and imaging. We demonstrate the strengths and weaknesses of the method using a circularly moving source with a fixed receiver.

Auralization↗

NASA NTRS1979

Spectral evolution of multiply impulsive solar bursts

Some results from the analysis of a set of multiply impulsive hard X-ray and microwave solar bursts are presented, showing that some bursts can exhibit widely different magnetic-field strengths at different times. Two categories of microwave spectral behavior are identified: those events during which the microwave turnover frequency (MTF) and spectral shape (SS) remain the same from peak to peak, and those during which the MTF and SS change significantly. These categories correspond to two classes of multiply impulsive bursts: those for which the emission can be characterized by a constant magnetic field and therefore a single source region, and those in which groups of component spikes appear to originate in regions of different magnetic-field strengths, corresponding to separate source regions which flare sequentially. With regard to the latter type, examples are presented, the discrete flaring regions are examined, and their spatial separations are estimated.

Karpen, J. T.↗

NASA NTRS1997

Relative Band Oscillator Strengths for Carbon Monoxide: Alpha (1)Pi-Chi (1)Sigma(+) Transitions

Band oscillator strengths for CO transitions between the electronic states A (l)Pi and X(1)Sigma(+) were measured via absorption with a synchrotron radiation source. When referenced to the well-characterized (5,0) band oscillator strength, our relative values for the (7,0) to (11,0) bands are most consistent with the recent experiments of Chan et al. and the theoretical predictions of Kirby & Cooper. Since the results from various laboratory techniques and theory now agree, analyses of interstellar CO based on absorption from A-X bands are no longer hindered by uncertainties in oscillator strength.

Federman, S. R.↗

NASA NTRS2017

Impact Delivery of Reduced Greenhouse Gases on Early MARS

While there is abundant evidence for flowing liquid water on the ancient Martian surface, a widely accepted greenhouse mechanism for explaining this in the presence of a faint young sun has yet to emerge. Gases such as NH3, CO2 alone, SO2, clouds, and CH4, have sustainability issues or limited greenhouse power. Recently, Ramirez et al. proposed that CO2-H2 atmospheres, through collision induced absorptions (CIA), could solve the problem if large amounts are present (1.3-4 bars of CO2, 50-20% H2). However, they had to estimate the strength of the H2- CO2 interaction from the measured strength of the H2- N2 interaction. Recent ab initio calculations show that the strength of CO2-H2 CIA is greater than Ramirez et al. assumed. Wordsworth et al. also calculated the absorption coefficients for CO2-CH4 CIA and show that on early Mars a 0.5 bar CO2 atmosphere with percent levels of H2 or CH4 can raise mean annual temperatures by tens of degrees Kelvin. Freezing temperatures can be reached in atmospheres containing 1-2 bars of CO2 and 2-10% H2 and CH4. The new work demonstrates that less CO2 and reduced gases are needed than Ramirez et al. originally proposed, which improves prospects for their hypothesis. If thick weakly reducing atmospheres are the solution to the faint young sun paradox, then plausible mechanisms must be found to generate and sustain the required concentrations of H2 and CH4. Possible sources of reducing gases include volcanic outgassing, serpentinization, and impact delivery; sinks include photolysis, oxidation, and hydrogen escape. The viability of the reduced greenhouse hypothesis depends, therefore, on the strength of these sources and sinks.

Martian surface↗

NASA NTRS1975

Anelastic deformation of boron fibers

The flexural deformation behavior of vapor-deposited boron fibers was examined from 100 to 1100 K by stress-relaxation and internal friction techniques. Only strong thermally-activated anelasticity was observed with no evidence of plasticity up to surface strains of 0.006. The parameters governing the relaxation processes within the anelastic spectra of as-received and annealed fibers were determined. These parameters were correlated with X-ray structure studies to develop preliminary models for the sources of boron's anelasticity. The large relaxation strengths of the dominant Ia processes coupled with their relaxation times and energies suggest a sliding mechanism between certain basic structural subunits common to both the beta-rhombohedral and vapor-deposited boron structures.

Dicarlo, J. A.↗

NASA NTRS1976

Correlation of internal surface turbulence with far-field noise of the augmentor wing propulsive-lift concept

A wind tunnel investigation was conducted to determine the nature, strength, and variation with airspeed of the acoustic sources of the augmentor wing propulsive-lift concept. The augmentor wing overall noise is dominated by the high frequency jet mixing noise characteristic of the lobed primary nozzle. The augmentor modifies the intensity and propagation characteristics of the jet sources, especially those that exist inside the augmentor. The interaction of the turbulent flow with the augmentor creates low-frequency, low-intensity surface noise and trailing edge noise. These sources dominate any jet mixing noise that is present at the low frequencies and could become significant if the jet noise was suppressed by treating the augmentor with a lining tuned to the jet noise source location. The far-field noise of the untreated augmentor is unaffected by airspeed; however, this may not be the case when the jet noise is suppressed, because the trailing edge surface pressure and correlations with far-field noise do show a reduction with forward speed.

Falarski, M. D.↗