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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 865 records · Page 48
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NASA NTRS1975

Recent developments in density, temperature and momentum fluctuation measurement

Attention is drawn to recent advancements in the fluctuating line-reversal temperature measurement, the development of the two-dimensional drag-sensing probe into a three-dimensional drag-sensing probe, and the fluctuating density gradient cross beam Schlieren technique. An experimental apparatus is explained whereby the temperature fluctuation in a pulsating air-fuel ratio Bunsen burner is measured by means of sodium D-line reversal methods with a new photoelectric circuit to obtain both fluctuating and mean temperature data. The three-D drag probe is made possible by a newly invented differential and total magnetic sensing system that separates signals due to three orthogonal movements so that the vectorial momentum fluctuation can be measured. In the case of the Schlieren technique, the effect of anisotropic density gradients with respect to the angle between the polarization plane and the knife edge of a laser Schlieren system is studied.

Battle, T. M.↗
NASA NTRS1975

The HEAO A-2 experiment on the spatial and spectral structure of the X-ray sky /0.2-60 keV/

The HEAO A-2 experiment is described which is designed to observe the spectral and spatial structure of cosmic X-radiation over the entire sky with the minimum sensitivity and cross checks required to achieve a number of objectives. Developments in X-ray astronomy are discussed which are relevant to the experiment, including setting a lower limit on the number of discrete sources contributing to the background flux, determining the spatial dependence of the flux, observations of the spectral components of discrete sources, and the study of X-ray absorption by interstellar gas and the atmospheres of binary stars associated with pulsating X-ray sources. It is shown that systematics-free measurements will be made by making simultaneous observations of single sources with several detectors, by using two-layer detectors to eliminate the effects of electron contamination, and by incorporating magnets into low-energy detectors to minimize electron contamination.

Boldt, E.↗
NASA NTRS1975

Optical and X-ray observations of the PSR 1913 + 16 field

We have obtained medium-resolution spectra in the yellow of seven stars in the error box of the binary radio pulsar PSR 1913 + 16, using the image-tube scanner at the Lick 3-m telescope. None of the objects is spectroscopically abnormal and thus a strong candidate for membership in the system. The data are used to establish the extinction in the field, which is modest for this low galactic latitude. For three of the stars, limits of the order V exceeding 23 mag on optical pulsations with the frequency of the radio pulsar are derived. X-ray observations of the field have been obtained in the 2.5-7.5 keV band, using the UCL experiment aboard OAO Copernicus. No source is detected, with a 2 sigma upper limit on the time-averaged flux of 1.0 times 10 to the -10th power ergs per sq cm per sec.

Davidsen, A.↗
NASA NTRS1975

Mean colors of Cepheids

Color observations of Cepheids can be interpreted by a color effective temperature relation to give different T sub e values for each kind of mean color. Here, theoretical colors from numerical integrations of Cepheid pulsations are used to determine the proper method of taking the color mean in order to get, by the color T sub e relation, the correct nonpulsating T sub e.

Cox, A. N.↗
NASA NTRS1975

Relativistic Electron Precipitation in the Auroral Zone

The energy spectra and pitch angle distributions of electrons in the energy range from 50 keV to 2 MeV were determined by a solid state electron energy spectrometer during the Relativistic Electron Precipitation (REP) event of 31 May 1972. The pitch angle distributions were determined from a knowledge of the rocket aspect and the direction in space of the earth's magnetic field. The rocket aspect determination was therefore treated in depth and a method was developed to compensate for the malfunctioning of the aspect magnetometer. The electron fluxes during the REP event were highly variable demonstrating correlated energy, flux, and pitch angle pulsations with time periods of less than one second. A theoretical model for the production of relativistic electrons was proposed. It follows from this model that, at comparatively low background electron densities, the anomalous Doppler resonance leads to the acceleration of near relativistic particles.

Simons, D. J.↗
NASA NTRS1975

CNO abundances and hydrodynamic models of the Nova outbursts. 4: Comparison with observations

A variety of observations of novae are discussed in light of theoretical models. It is proposed that the nearly constant bolometric luminosity of FH Ser originates in the non-degenerate hydrogen-burning region at the bottom of the hydrogen-rich envelope which remains after the primary ejection. The shift of the wavelength of peak emission from the visual to shortward of the ultraviolet is caused by the decrease of the photospheric radius of the remnant envelope as the bolometric luminosity stays nearly constant. The oscillations in the light curve of GK Per during the transition stage can be explained by a pulsation of the remnant envelope when it is the size of the Roche lobe. The CNO over-abundances in novae reported by various observers are strongly suggestive of this nova mechanism. Finally, the implications of the upper limits of C-13 and N-15 in DQ Her are discussed.

Sparks, W. M.↗
NASA NTRS1976

Blood flow

A heuristic treatment of blood flow in the heart and the aorta together with some of the main branches considers the effects of fluid viscosity and vessel elasticity as well as pressure distribution in the typical pulsating flow.

Jones, R. T.↗
NASA NTRS1975

Observation of soft X-rays from cosmic sources

A binary X-ray source, an extended extragalactic X-ray source and several nearby stars were surveyed for X-ray emission. The energy spectrum and time structure of X-ray flux from the binary source, Her X-l, was investigated in the range from 0.15 to 6 KeV. This source was observed at a binary phase of 0.18 with the system near elongation normal to the line of sight. Intense pulsations were observed in optical emission lines near this binary phase. The spectrum and angular distribution of X-ray emission from the X-ray source in the Virgo Cluster of Galaxies, near M 87, was also observed. In addition, the stars Alpha Leo, Zeta Her, and Epsilon Vir were investigated. Epsilon Aur and Alpha Aur were also scanned. These stars were studied since there is increasing evidence that such objects may be transient sources of soft X-rays.

Catura, R. C.↗
NASA NTRS1976

Spectral variability in the X-ray pulsar GX 1+4

Observations of the galactic center region, hard X-ray source GX 1+4 by the GSFC X-ray spectroscopy experiment on OSO-8 confirm that GX 1+4 is a slow X-ray pulsar. The amount of absorption by cold matter in the spectrum of GX 1+4 varies significantly within a 24 hour period, behavior typical of many X-ray binary systems. The light curve for the pulsations from GX 1+4 appears to be energy dependent.

Becker, R. H.↗
NASA NTRS1976

Centaurus X-3: The observational picture

Observations of Centaurus X-3 are briefly reviewed. The composition of the neutron star, optical light curves, and X-ray pulsations are among the topics discussed.

Mauder, H.↗
NASA NTRS1976

Recent Uhuru results on Centaurus X-3

The current status of the analysis of Cen X-3 data from Uhuru concerning pulsations, orbital period and eccentricity, and extended lows, are reviewed. The pulse period decreases irregularly. The pulsed fraction (2-7 keV) is 70%-90% for single pulses but significantly less for superpositions of pulses, due to variability in shape. The pulses are narrower at higher energies with a correlated increase in fraction pulsed. The orbital period is found to both decrease and increase with p/p on the order of a few times 0.00001/year. A three sigma upper limit on the eccentricity of 0.003 is obtained; if no significant periastron motion is allowed over two years, the upper limit becomes 0.0016. The orbital period is found to be detectable during some extended lows but with a significantly decreased ratio of eclipsed to non-eclipsed intensity. Two transitions between normal high states and extended lows are studied, and a consistent model is obtained in which extended lows are caused by both burying the source in an increased stellar wind from the companion, and starving the source by decreasing the stellar wind. Changes in fraction pulsed during transitions and systematic differences in the harmonic content of the pulses are also found.

Schreier, E. J.↗
NASA NTRS1976

OSO-8 GSFC results on Cen X-3

Spectra of Cen X-3 during eclipse, in transition out of eclipse, and during several later phases of the binary orbit were obtained from quick look data of the July 16-25, 1975 observation by the Goddard X-ray spectroscopy experiment on OSO-8. In the high state there was no absorption turn over. Pulsations were present at least to 23 keV. The spectrum at the pulse minimum was flatter above 7 keV than that of the pulse peak. In transition out of eclipse Cen X-3 emerged above a small low energy flux seen during eclipse. The observations appear to indicate absorption by cold and ionized matter and the presence of iron in the companion's atmosphere. Decreased intensities were observed at late phases of some binary orbits in some cases corresponding to dips. Absorption appears although the low energy component remains. Variable features may be interpretable as absorption and emission by iron and possibly other trace elements.

Swank, J. H.↗
NASA NTRS1976

Preliminary Results from the European Space Agency's COS-B satellite for gamma-ray astronomy

The COS-B satellite carries a single experiment, capable of detecting gamma rays with energies greater than 30 MeV. Its objectives are to study the spatial, energy, and time characteristics of high energy radiation of galactic and extragalactic origin. The capability to search for gamma ray pulsations is enhanced by the inclusion in the payload of a proportional counter sensitive to X-rays of 2-12 Kev. The experiment was calibrated using particle accelerators. The results of these measurements are presented and the performance of the system in orbit is discussed.

Swanenburg, B.↗
NASA NTRS1975

Micropulsations in the morning sector. II - Satellite observations of 10to 45-s waves at synchronous orbit, ATS 1

A study of 13 wave events having 10- to 45-s periods and observed by ATS 1 in the morning sector reveals that these events, which have been called band-limited pulsations and are thought to be related to Pi 1, appear actually to be Pc 3. Digital power-spectral and coherency analysis was used to determine the characteristics of the wave activity. The average peak frequency of the events (about 0.04 Hz) and their generally narrow-band nature correspond closely with the characteristics of Pc 3. The local-time distribution of the events (peaking at 0900 LT) and their less than complete association with substorms also correspond more closely with Pc 3 characteristics. The orientation of the major axis of the polarization ellipse for these events was predominantly azimuthal, which agrees more closely with the east-west polarization of Pi 1 observed on the ground. However, some examples of radial orientation were observed in the satellite data.

Arthur, C. W.↗
NASA NTRS1975

Average 2-6 keV pulse shapes of Hercules X-1 during the January 1972 'on' state

The available data on the Uhuru satellite sightings of observably bright ('on' state) Her X-1 during January 1972 are divided into eight intervals between successive eclipses. The average pulse shapes obtained are discussed. It is shown that the average pulse shape varies little during most of the 'on' state. However, during about the last three days of the 'on' state, the pulsations almost completely disappear. The results appear to support a class of models in which the 35-day cycle is due to variable obscuration of Her X-1 by a precessing accretion disk or other matter within the system.

Joss, P. C.↗
NASA NTRS1976

Electron precipitation in the postmidnight sector of the auroral zones

Measurements of the angular distributions and energy spectra of electron intensities within the energy range 50 eV to 15 keV with electrostatic analyzer arrays on board the low-altitude satellite Injun 5 are reported for the postmidnight sector of the auroral zones during the high-intensity events accompanying magnetic substorms. Precipitation features on closed terrestrial field lines well equatorward of the trapping boundary for electrons with energies greater than 45 keV are examined. Precipitation of low-energy electron intensities was characterized by isotropy for all pitch angles outside the atmospheric backscatter cone. The region of electron precipitation observed is associated with the diffuse aurora and with pulsating aurora in the postmidnight sector. Similar variations of the energetic electron intensities with energies above 45 keV were observed in the regions of fluctuating energy fluxes of low-energy electrons associated with auroral luminosity. The increases of energetic electron intensities were not coincident with those of the principal energy fluxes into the atmosphere, except when the average electron energy for the energy fluxes was unusually high, i.e., in the 10-keV range. Precipitation of electron intensities within these energy ranges is consistent with strong pitch angle diffusion of electron intensities near or at the magnetic equator by high-frequency wave turbulence, the effectiveness of which is modulated by perturbations attributable to micropulsations.

Frank, L. A.↗
NASA NTRS1975

Unsteady flow in cavitating turbopumps

Unsteady flow in a cavitating axial inducer pump is analyzed with the help of a simple two-dimensional cascade model. This problem was motivated by a desire to study the effect of unsteady cavitation on the so-called POGO instability in the operation of liquid rocket engines. Here, an important feature is a closed loop coupling between several different modes of oscillation, one of which is due to the basic unsteady characteristics of the cavitation itself. The approaching and leaving flow velocities up- and downstream of the inducer oscillate, and the cavity-blade system participates dynamically with the basic pulsating flow. In the present work, attention is focused on finding a transfer matrix that relates the set of upstream variables to those downstream. This quantity, which is essentially equivalent to cavitation compliance in the quasi-static analyses, is found to be complex and frequency dependent.

Kim, J. H.↗
NASA NTRS1975

Distribution of cosmic gamma rays in the galactic anticenter region as observed by SAS-2

The high energy (above 35 MeV) gamma ray telescope flown on the second Small Astronomy Satellite has collected over one thousand gamma rays from the direction of the galactic anticenter. In addition to the diffuse galactic emission the distribution indicates a strong pulsed contribution from the Crab nebula with the same period and phase as the NP0532 pulsar. There also seems to be an excess in the direction of (gal. long. ? 195 deg; gal. lat ? +5 deg) where there is a region containing old supernova remnants. Search for gamma ray pulsations from other pulsars in the region do not show any statistically significant signal. The general intensity distribution of the gamma rays away from the plane appear to be similar to nonthermal radio emission brightness contours.

Kniffen, D. A.↗