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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 703 records · Page 39
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NASA NTRS1984

Direct evidence for solar wind control of Jupiter's hectometer-wavelength radio emission

Observations of the solar wind close to Jupiter by the Voyager 1 and Voyager 2 spacecraft in 1978 and 1979 are compared with the hectometer-wavelength radio emission from the planet. A significant positive correlation is found between variations in the solar wind plasma density at Jupiter and the level of Jovian radio emission output. During the 173-day interval studied for the Voyager 2 data the radio emission displayed a long-term periodicity of about 13 days, identical to that shown by the solar wind density at Jupiter and consistent with the magnetic sector structure association already proposed for ground-based observations of the decameter-wavelength emission.

Desch, M. D.↗
NASA NTRS1984

Direct evidence for solar wind control of Jupiter's hectometer-wavelength radio emission

Observations of the solar wind close to Jupiter, by the Voyager 1 and Voyager 2 spacecraft in 1978 and 1979, are compared with the hectometer wavelength radio emission from the planet. A significant positive correlation is found between variations in the solar wind plasma density at Jupiter and the level of Jovian radio emission output. During the 173-day interval studied for the Voyager 2 data, the radio emission displayed a long term periodicity of about 13 days, identical to that shown by the solar wind density at Jupiter and consistent with the magnetic sector structure association already proposed for groundbased observations of the decameter wavelength emission.

Desch, M. D.↗
NASA NTRS1985

Observation of pick-up ions in the solar wind: Evidence for the source of the anomalous cosmic ray component?

Singly ionized energetic helium has been observed in the solar wind by using the time of flight spectrometer SULEICA on the AMPTE/IRM satellite between September and December, 1984. The energy density spectrum shows a sharp cut off which is strongly correlated with the four fold solar wind bulk energy. The absolute flux of the He(+)ions of about 10000 ion/sq cm.s is present independent of the IPL magnetic field orientation. The most likely source is the neutral helium of the interstellar wind which is ionized by solar UV radiation. It is suggested that these particles represent the source of the anomalous cosmic ray component.

Hovestadt, D.↗
NASA NTRS1984

Rocket observations of the diffuse ultraviolet background

The objective of the experiment reported here was to obtain additional information on the absolute intensity level and spatial variation of the diffuse ultraviolet background and thereby gain insight into the origin of this radiation. The experiment used three ultraviolet sensitive photometers placed in the focal plane of a 95-cm, f/2.8 normal incidence telescope flown on board an Aries sounding rocket. The measured intensities clearly refute the hypothesis of an isotropic background, the intensities of the high galactic latitude being definitely lower than the intensities seen at intermediate latitudes. Moreover, the count rates in all three channels along the slow scan exhibit local enhancements as well as an overall trend. In general, the spatial variations exhibited by the data correlate with the line of sight of neutral hydrogen column density as determined from 21-cm radio observations. This fact demonstrates that there is a galactic component to the diffuse ultraviolet radiation field.

Jakobsen, P.↗
NASA NTRS1985

MPD thruster performance - Propellant distribution and species effects

Previous research has shown that MPD thruster performance, as measured by thrust, specific impulse, and efficiency, is limited by a so-called 'onset' current level. Experimental results are presented which show that the onset current level varies with the radial position of mass injection. Specifically, mass injection into either of two zones results in drastically different performance for both argon and xenon propellants. This difference in performance is evidenced by the onset current levels, the onset V-J signatures, and the overall V-J characteristics. The behavior of the thruster with the total mass flow split between the two zones follows a transition between the zonal behavioral limits. The behavior of propellant mixtures also follows a transition between the behavior of the individual propellant species. The flow region between the two zones is characterized by a particle number density discontinuity, a large axial current density, and a large electron Hall parameter, suggesting a possible correlation between observed onset phenomena and a shear-flow discontinuity located in the region between the two zones.

Kelly, A. J.↗
NASA NTRS1986

On Io's control of Jovian decametric radio emissions

Io's control of Jovian decametric radio emission (DAM) has been attributed to Io distorting the electron distribution in the inner Jovian magnetosphere. Observations of Faraday rotation in DAM are used to determine the properties of the electron distribution before and after its interaction with Io. It is shown that there is an enhancement in the density of the energetic component in the Io plasma torus correlated with certain Jovian longitude. Io's interaction with this energetic component can produce heating of this component. The Io-controlled emission is attributed to enhanced emission from the heated electrons moving down the field lines to Jupiter.

Winglee, R. M.↗
NASA NTRS1986

The dynamics of Herbig-Haro objects

Radial-velocity and proper-motion information on Herbig-Haro (HH) objects is analyzed for clues to the character of the supersonic flows that produce the objects. The correlations among space velocities, excitation states, internal velocity dispersions, electron densities, and positions relative to the exciting stars for the emission knots of HH 1 and HH 2 is examined. Whereas the interstellar-bullet model may account for most of the phenomena in the HH 1-HH 2 system, HH 43 is found to show characteristics of a stellar wind shock against an obstacle cloudlet. By contrast, the HH 46-HH 47 system exhibits a continuous, well-collimated jet of emission with knots that may be due to instabilities in the confined, supersonic flow.

Schwartz, R. D.↗
NASA NTRS1989

Correlation studies between solar wind parameters and the decimetric radio emission from Jupiter

Results of a study comparing long-term time variations in Jupiter's synchrotron radio emission with a variety of solar wind parameters and the 10.7 cm solar flux are reported. Data from 1963 through 1985 were analyzed, and the results suggest that many solar wind parameters are correlated with the intensity of the synchrotron emission produced by the relativistic electrons in the Jovian Van Allen radiation belts. Significant nonzero correlation coefficients appear to be associated with solar wind ion density, ram pressure, thermal pressure, flow velocity, momentum, and ion temperature. The implication of these results is that the solar wind is influencing the supply and/or loss of electrons to Jupiter's inner magnetosphere.

Bolton, S. J.↗
NASA NTRS1990

A model for the distribution of material generating the soft X-ray background

The observational evidence relating to the soft X-ray diffuse background is discussed, and a simple model for its source and spatial structure is presented. In this simple model with one free parameter, the observed 1/4 keV X-ray intensity originates as thermal emission from a uniform hot plasma filling a cavity in the neutral material of the Galactic disk which contains the sun. Variations in the observed X-ray intensity are due to variations in the extent of the emission volume and therefore the emission measure of the plasma. The model reproduces the observed negative correlation between X-ray intensity and H I column density and predicts reasonable values for interstellar medium parameters.

Snowden, S. L.↗
NASA NTRS1991

Exact hierarchical clustering in one dimension

The present adhesion model-based one-dimensional simulations of gravitational clustering have yielded bound-object catalogs applicable in tests of analytical approaches to cosmological structure formation. Attention is given to Press-Schechter (1974) type functions, as well as to their density peak-theory modifications and the two-point correlation function estimated from peak theory. The extent to which individual collapsed-object locations can be predicted by linear theory is significant only for objects of near-characteristic nonlinear mass.

Williams, B. G.↗
NASA NTRS1951

Correlation of physical properties with molecular structure for some dicyclic hydrocarbons having high thermal-energy release per unit volume

As part of a program to study the correlation between molecular structure and physical properties of high-density hydrocarbons, the net heats of combustion, melting points, boiling points, densities, and kinematic viscosities of some hydrocarbons in the 2-n-alkylbiphenyl, 1,1-diphenylalkane, diphenylalkane, 1,1-dicyclohexylalkane, and dicyclohexylalkane series are presented.

Wise, P H↗
NASA NTRS1996

Electromagnetic Compatibility Testing Studies

This report discusses the results on analytical models and measurement and simulation of statistical properties from a study of microwave reverberation (mode-stirred) chambers performed at Texas Tech University. Two analytical models of power transfer vs. frequency in a chamber, one for antenna-to-antenna transfer and the other for antenna to D-dot sensor, were experimentally validated in our chamber. Two examples are presented of the measurement and calculation of chamber Q, one for each of the models. Measurements of EM power density validate a theoretical probability distribution on and away from the chamber walls and also yield a distribution with larger standard deviation at frequencies below the range of validity of the theory. Measurements of EM power density at pairs of points which validate a theoretical spatial correlation function on the chamber walls and also yield a correlation function with larger correlation length, R(sub corr), at frequencies below the range of validity of the theory. A numerical simulation, employing a rectangular cavity with a moving wall shows agreement with the measurements. The determination that the lowest frequency at which the theoretical spatial correlation function is valid in our chamber is considerably higher than the lowest frequency recommended by current guidelines for utilizing reverberation chambers in EMC testing. Two suggestions have been made for future studies related to EMC testing.

Trost, Thomas F.↗
NASA NTRS1979

Maximum Likelihood Factor Analysis of the Effects of Chronic Centrifugation on the Structural Development of the Musculoskeletal System of the Rat

At the age of 30 days female Sprague-Dawley rats were placed on a 3.66 m radius centrifuge and subsequently exposed almost continuously for 810 days to either 2.76 or 4.15 G. An age-matched control group of rats was raised near the centrifuge facility at earth gravity. Three further control groups of rats were obtained from the animal colony and sacrificed at the age of 34, 72 and 102 days. A total of 16 variables were simultaneously factor analyzed by maximum-likelihood extraction routine and the factor loadings presented after-rotation to simple structure by a varimax rotation routine. The variables include the G-load, age, body mass, femoral length and cross-sectional area, inner and outer radii, density and strength at the mid-length of the femur, dry weight of gluteus medius, semimenbranosus and triceps surae muscles. Factor analyses on A) all controls, B) all controls and the 2.76 G group, and C) all controls and centrifuged animals, produced highly similar loading structures of three common factors which accounted for 74%, 68% and 68%. respectively, of the total variance. The 3 factors were interpreted as: 1. An age and size factor which stimulates the growth in length and diameter and increases the density and strength of the femur. This factor is positively correlated with G-load but is also active in the control animals living at earth gravity. 2. A growth inhibition factor which acts on body size, femoral length and on both the outer and inner radius at mid-length of the femur. This factor is intensified by centrifugation.

Amtmann, E.↗
NASA NTRS1974

San Marco C-2 Explorer

The San Marco C-2 spacecraft will be launched no earlier than 18 February 1974 from the San Marco Range located off the coast of Kenya, Africa, by a Scout launch vehicle. The launch will be conducted by an Italian crew. The San Marco C-2 is the fourth cooperative satellite project between Italy and the United States. The purpose of the mission is to obtain measurements of the diurnal variations of the equatorial neutral atmosphere density, composition, and temperature and to use these data for correlation with AE-C (Explorer 51) data for studies of the physics and dynamics of the thermosphere. The San Marco C-2 project is a joint undertaking of the National Aeronautics and Space Administration (NASA) and the Italian Space Commission officially initiated with a Memorandum of Understanding in August of 1973. Project management responsibility for the Italian portion of the project has been assigned to the Centro Ricerche Aerospaziali (CRA) while the Goddard Space Flight Center (GSFC) has responsibility for the United States portion.

Source record↗
NASA NTRS2008

Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit

A predictive tool was developed to estimate the low Earth orbit (LEO) atomic oxygen erosion yield of polymers based on the results of the Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment flown as part of the Materials International Space Station Experiment 2 (MISSE 2). The MISSE 2 PEACE experiment accurately measured the erosion yield of a wide variety of polymers and pyrolytic graphite. The 40 different materials tested were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The resulting erosion yield data was used to develop a predictive tool which utilizes chemical structure and physical properties of polymers that can be measured in ground laboratory testing to predict the in-space atomic oxygen erosion yield of a polymer. The properties include chemical structure, bonding information, density and ash content. The resulting predictive tool has a correlation coefficient of 0.914 when compared with actual MISSE 2 space data for 38 polymers and pyrolytic graphite. The intent of the predictive tool is to be able to make estimates of atomic oxygen erosion yields for new polymers without requiring expensive and time consumptive in-space testing.

Bank, Bruce A.↗
NASA NTRS2019

The Far-Infrared Polarization Spectrum of Ρ Ophiuchi A from HAWC+/SOFIA Observations

We report on polarimetric maps made with HAWC+/SOFIA toward ρ Oph A, the densest portion of the ρ Ophiuchi molecular complex. We employed HAWC+ bands C (89 μm) and D (154 μm). The slope of the polarization spectrum was investigated by defining the quantity R(sub DC) = p(sub D)/p(sub C), where p(sub C) and p(sub D) represent polarization degrees in bands C and D, respectively. We find a clear correlation between R(sub DC) and the molecular hydrogen column density across the cloud. A positive slope (R(sub DC) > 1) dominates the lower-density and well- illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope (R(sub DC) < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of R(sub DC) is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.

Santos, Fabio P.↗
NASA NTRS2018

The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium

Whether stars could have driven the reionization of the intergalactic medium depends critically on the proportion of ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst (GRB) afterglows can be used to estimate the opacity to extreme ultraviolet (EUV) radiation along the lines-of-sight to the bursts. Assuming that long-duration GRBs trace the locations of the massive stars dominating EUV production, the average escape fraction of ionizing radiation can be calculated independently of galaxy size or luminosity. Here we present a compilation of HI column density (N(HI)) measures for 140 GRBs in the range 1.6 < z <6.7. Although the sample is heterogeneous, in terms of spectral resolution and signal-to-noise ratio, fits to the Ly α absorption line provide robust constraints on N(HI), even for spectra of insufficient quality for other purposes. Thus we establish an escape fraction at the Lyman limit of {f(esc)} ≈ 0.005, with a 98 per cent confidence upper limit of {f(esc)} ≈ 0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget at z < 5. At higher redshifts firm conclusions are limited by the small size of the GRB sample (7/140), but any decline in average HI column density seems to be modest. We also find no significant correlation of N(HI) with galaxy UV luminosity or host stellar mass. We discuss in some detail potential biases and argue that, while not negligible, systematic errors in f(esc) are unlikely to be more than a factor ∼2 in either direction, and so would not affect the primary conclusions. Given that many GRB hosts are low-metallicity dwarf galaxies with high specific star-formation rates, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the Universe.

N R Tanvir↗
NASA NTRSDate not supplied

Preparing Quantum Many-Body Scar States on Quantum Computers

Quantum many-body scar states are highly excited eigenstates of many-body systems that exhibit atypical entanglement and correlation properties relative to other eigenstates at the same energy density. Scar states also give rise to infinitely long-lived coherent dynamics when the system is prepared in a special initial state having finite overlap with them. Many models with exact scar states have been constructed, but the fate of scarred eigenstates and dynamics when these models are perturbed is difficult to study with classical computational techniques. In this work, we propose state preparation protocols for individual scar states in a particular model, as well as superpositions of them that give rise to coherent dynamics. For superpositions of scar states, we propose both a linear depth unitary and a finite-depth nonunitary state preparation protocol, the latter of which uses measurement and postselection to reduce the circuit depth. For individual scarred eigenstates, we propose a circuit architecture with polynomial depth. We also provide proof of principle implementations of these protocols on superconducting quantum hardware.

Quantum Computing↗