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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Observations of the 4.8-hour variations of Cygnus X-3 above 7 keV from the OSO-7

Results of observations made (during the period from June 30 to July 5, 1972) of Cyg X-3 with the UCSD OSO-7 X-ray telescope in the range from about 7 to 100 keV. The 4.8-hour variation was detected in the 6.6-21.2 keV range, and the ratio of high intensity to mean intensity was 1.52 plus or minus 0.16. In the 21.2-97.8 keV range no 4.8-hour variation in phase with the 6.6-21.2 keV variation could be detected, and the ratio at the phase of high intensity to the mean intensity was 0.6 plus or minus 0.4.

Ulmer, M. P.↗
NASA NTRS1962

Time-Dependent Structure of the Upper Atmosphere

The physical properties of the upper atmosphere are determined mainly by heat conduction, the heat sources and the barometric law. An analysis of the integro-differential equation which describes these physical processes has been carried out. It is found that heating of the thermosphere due to absorption of the solar extreme ultraviolet (EUV) radiation alone cannot explain the observed diurnal variation of density and temperature, since it would yield a maximum of these properties at about 17h local time, instead of 14h where it is observed. Secondly, if the EUV flux is adjusted to give the observed average temperature, then the diurnal variation in density would be much too large compared with the observed amplitude. Thirdly, it would require an extremely high efficiency for the conversion of EUV radiation into heat, if we compare the required flux with Hinteregger's measurements of the EUV flux. Thus, it is necessary to have another heat source in addition to the heating due to absorption of EUV radiation. If an additional beat source is used, which has a maximum at about 9h local time and a flux of 1 erg cm−1 sec−1, a time-dependent model of the upper atmosphere is obtained that is in good agreement with the observed densities. There is evidence that this additional heat source derives its energy ultimately from the solar corpuscular radiation. In this paper we present the results of calculations for a model in the equatorial and temperature zones of the earth, for those times when the average solar activity corresponds to a solar radiation flux of 200×110−22 Wm−2 (cps)−1 at 10.7-cm wavelength. The physical properties (temperature, density, pressure, scale height, mean molecular weight and the number densities of N2, O2, O, He and H) are given as a function of local time and for the altitudes between 120 km and 2050 km.

ATMOSPHERE↗
DOE OSTI2022

Effect of injected flux and current temporal phasing on self-organization in the HIT-SI3 experiment

The HIT-SI3 device at the University of Washington uses three oscillating inductive helicity injectors to form and sustain spheromak plasma equilibria. By adjusting the temporal phase of the injector waveforms with respect to each other, the toroidal spectrum of the imposed perturbations can be controlled. Using a recently implemented GPU-based control system, the available mode spectra were explored experimentally by scanning the space of relative injector phasing. In this space, significant variation in the toroidal mode spectrum ($n$ = 1, 2, 3) of the perturbations was observed. Additionally, variation in characteristics of driven equilibria was also observed, including a ≈ $30$% range in toroidal current gain ($I$ $Φ$ / $I$ $Inj$ ). Experimental results are compared with both a composite-equilibria and nonlinear dynamic model, including extended MHD simulations using the NIMROD code and composite Taylor state equilibria computed using the PSI-Tet code. In conclusion, qualitative agreement is seen with the nonlinear models, but not with composite-equilibria models, suggesting the use of nonlinear models to better capture observed plasma dynamics and provide predictive use for future experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1976

Magnetic shadowing of charged particles by an extended surface

The problem of particle shadowing by the lunar surface is examined. Shadow zones are obtained analytically for small-aperture detectors on an infinite flat surface and are shown to be in good agreement with those obtained by numerical trajectory tracing. The shadow zones cover about half of all possible external field orientations for a vertical detector, which may result in serious underestimations of the frequency of observation of a particular plasma region. Shadowing may cause wide variations between observed and actual pitch angle distributions even in the case of multiple- or large-aperture detectors. Since the particle flux can be considered approximately isotropic only for magnetic fields within 35 deg of the surface normal, the electron flux to the surface may be overestimated in current balance calculations ignoring the magnetic field direction. In addition, photoelectrons may be returned to the surface by the magnetic field.

Reiff, P. H.↗
NASA NTRS1993

Geocenter location and variations in earth orientation using global positioning system measurements

We have studied the use of GPS ground and flight tracking data to measure short-period earth orientation variations and changes in geocenter location. Comparisons between GPS-estimated earth rotation variations and those calculated from ocean tide models suggest that observed subdaily variations in earth rotation are dominated by oceanic tidal effects. Our preliminary GPS estimates for geocenter location agree with an independent satellite laser ranging estimates to 10-15 cm. Covariance analysis predicts that temporal resolution of GPS estimates for earth orientation and geocenter improves significantly when data collected from low earth-orbiting satellites as well as from ground sites are combined. The low-earth GPS tracking data enhance the accuracy and resolution for measuring high-frequency global geodynamical signals over time scales less than 1 day.

Malla, R. P.↗
NASA NTRS1980

ISEE-3 measurements of solar energetic particle composition

Preliminary observations of energetic particles from solar flares beginning on September 23 and November 10, 1978 are reported. The measurements were made from the ISEE-3 spacecraft using very thin, large area solid-state detectors. Charge composition was measured for all elements from Z = 2 to Z = 26 above approximately 2 MeV/nucleon. More than 100,000 nuclei with Z greater than 2 were pulse-height analyzed during the course of the first event, while the second was substantially smaller. These good statistics enable the observation of variations in composition at low energies as a function of time. For example, the Fe/O ratio (2.0-3.1 MeV/n) was observed in the September event to decrease by a factor of approximately 5. By contrast, this same ratio increased by a factor of approximately 1.5 during the November 10 event. Similar variations have been reported earlier by Scholer et al. (1978). These authors, however were unable to observe the He/O ratio which has now been observed also to show significant variation.

Von Rosenvinge, T. T.↗
NASA NTRS1979

Volatiles in Chainpur chondrules

A study of volatile element concentrations in individual chondrules in the Chainpur LL3 chondrite is presented. Volatile elements differing in geochemical behavior tended to vary randomly and correlated variations were observed only for those elements inferred to occupy similar mineral sites. Variations in Co and Ni in kamacite show that metal in chondrule interiors has not approached equilibrium, and that postformational element distribution has mainly altered siderophile concentrations in surface metal grains, and has probably left ionic species unaltered. Etching to remove 3 to 5% of the chondrule dissolved siderophiles, enhanced Zn and Na volatiles relative to nonvolatile Cr in the etch, and produced a large Cd enhancement. If metamorphic redistribution of nonsiderophile volatiles was neglible, their high concentrations are inconsistent with chondrule formation by direct condensation, and models involving sudden melting of preexisting solids can explain the observations but require rapid cooling to prevent volatile loss.

Grossman, J. N.↗
NASA NTRS1994

Local fluctuations of ozone from 16 km to 45 km deduced from in situ vertical ozone profile

A vertical ozone profile obtained by an in situ ozone sonde from 16 km to 45 km, has allowed to observe local ozone concentration variations. These variations can be observed, thanks to a fast measurement system based on a UV absorption KrF excimer laser beam in a multipass cell. Ozone standard deviation versus altitude calculated from the mean is derived. Ozone variations or fluctuations are correlated with the different dynamic zones of the stratosphere.

Moreau, G.↗
NASA NTRS1986

Physical aging in epoxy matrices and composites

Postcured specimens of Thornell 300 carbon-fiber/Fiberite 934 epoxy as well as Fiberite 934 epoxy resin were quenched from above the glass transition temperature and annealed at 140, 110, or 80 C for times up to 100,000 min. No weight gain or loss was observed during annealing at these temperatures, but significant time-dependent variations were observed in density, modulus, hardness, damping, moisture absorption ability, and thermal expansion characteristics. The relations between the excess thermodynamic properties of epoxy glasses and their time-dependent behavior are discussed. The discussion is illustrated by results obtained by differential scanning calorimetry, dynamic mechanical analysis, tensile testing, solid state nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering.

Kong, Eric Siu-Wai↗
NASA NTRS1989

Surface brightness fluctuations and the distance to the Virgo Cluster

Preliminary results from a project to measure the fluxes of giant stars in M32, NGC 3379, and five Virgo Cluster galaxies are presented. Since the Virgo Cluster galaxies are approximately equidistant, variations in observed fluctuation amplitude from galaxy to galaxy can be ascribed to variations in absolute luminosity of the giant stars in the galaxies. Assuming a distance of 0.72 Mpc for M32 and correcting for the color effect in m-bar, the typical brightness of giant stars, distances of 9 Mpc for NGC 3379 and 14 Mpc for Virgo, accurate to about 10 percent, are derived. This is used to find a Hubble constant of 88 km/s/Mpc. The method can be used to measure m-bar in galaxies at least 40-50 Mpc distant.

Tonry, John L.↗
DOE OSTI2022

Dissolved oxygen sensor in an automated hyporheic sampling system reveals biogeochemical dynamics

Many river corridor systems frequently experience rapid variations in river stage height, hydraulic head gradients, and residence times. The integrated hydrology and biogeochemistry of such systems is challenging to study, particularly in their associated hyporheic zones. Here we present an automated system to facilitate 4-dimensional study of dynamic hyporheic zones. It is based on combining real-time in-situ and ex-situ measurements from sensor/sampling locations distributed in 3-dimensions. A novel dissolved oxygen (DO) sensor was integrated into the system during a small scale study. We measured several biogeochemical and hydrologic parameters at three subsurface depths in the riverbed of the Columbia River in Washington State, USA, a dynamic hydropeaked river corridor system. During the study, episodes of significant DO variations (~+/- 4 mg/l) were observed, with minor variation in other parameters (e.g., <~+/-0.15 mg/l NO 3 ). DO concentrations were related to hydraulic head gradients, showing both hysteretic and non-hysteretic relationships with abrupt (hours) transitions between the two types of relationships. The observed relationships provide a number of hypotheses related to the integrated hydrology and biogeochemistry of dynamic hyporheic zones. We suggest that preliminary high-frequency monitoring is advantageous in guiding the design of long term monitoring campaigns. The study also demonstrated the importance of measuring multiple parameters in parallel, where the DO sensor provided the key signal for identifying/detecting transient phenomena.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1989

Observed solar near UV variability: A contribution to variations of the solar constant

Continuous Measurements of the Solar UV have been made by an instrument on the Solar Mesosphere Explorer (SME) since October 1981. The results for the wavelength interval 200 to 300 nm show an irradiance decrease to a minimum in early 1987 and a subsequent increase to mid-April 1989. The observed UV changes during part of solar cycles 21 to 22 represent approx. 35 percent (during the decreasing phase) and 25 percent (during the increasing phase) of the observed variations of the solar constant for the same time period as the SME measurements.

London, Julius↗
NASA NTRS1982

On the variability of LSI+61 deg 303 (identical with GT 0236)

Out of six long and six short wavelength observations, one spectrum exhibits a significant photometric variation: or approximately 20%. Interpreting the continuum as due to superposition of an early B main sequence star plus a gaseous component contributing at lambda 2000 A, the wavelength dependence of the variation suggests that it derives from the latter component. The data indicate that if the observed variation is phase dependent, a minimum should occur between phases 0.8 and 0.2. However, since the variation is observed in only one spectrum, it may well be erratic.

Tanzi, E. G.↗
NASA NTRS1992

The optical variability of PKS 2155 - 304

Results of photometric monitoring of the BL Lacertae object PKS 2155 - 304 between 1979 and 1990 are presented. Optical variations were observed on time scales ranging from several minutes to several years. The variations detected with time scales on the order of minutes are among the fastest optical variations detected for a BL Lacertae object. These rapid variations provided constraints on the mass of the supermassive black hole, assumed to be present at the center of the object, of the range between 5.5 +/-0.4 x 10 exp 8 and 8.1 +/-1.0 x 10 exp 9 solar masses. The results indicate that the characteristic variability time scale for the optical variability is shorter than the characteristic variability time scale established for the UV of approximately 50 d reported by Treves et al. (1989).

Carini, Michael T.↗
NASA NTRS1993

Spectral variations of LMC X-3 observed with Ginga

The prime black hole candidate LMC X-3 was observed over three years with the Ginga satellite, and a characteristic spectral variation was found accompanying the periodic intensity variation of about 198 (or possibly about 99) days (Cowley et al., 1991). The energy spectrum of LMC X-3 consists of the soft, thermal component and the hard, power-law component, which are respectively dominant below and above about 9 keV. The soft component, which carries most of the X-ray intensity, shows a clear correlation between the intensity and the hardness, while the hard component varies independently of the soft component. It was found that the spectral variation of the soft component is well described by an optically thick accretion disk model with a remarkably constant innermost radius and variable mass accretion rate. The constancy of the innermost radius suggests it is related to the mass of the central object.

Ebisawa, Ken↗