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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Photoballistics of volcanic jet activity at Stromboli, Italy

Two night eruptions of the volcano Stromboli were studied through 70-mm photography. Single-camera techniques were used. Particle sphericity, constant velocity in the frame, and radial symmetry were assumed. Properties of the particulate phase found through analysis include: particle size, velocity, total number of particles ejected, angular dispersion and distribution in the jet, time variation of particle size and apparent velocity distribution, averaged volume flux, and kinetic energy carried by the condensed phase. The frequency distributions of particle size and apparent velocities are found to be approximately log normal. The properties of the gas phase were inferred from the fact that it was the transporting medium for the condensed phase. Gas velocity and time variation, volume flux of gas, dynamic pressure, mass erupted, and density were estimated. A CO2-H2O mixture is possible for the observed eruptions. The flow was subsonic. Velocity variations may be explained by an organ pipe resonance. Particle collimation may be produced by a Magnus effect.

Chouet, B.↗
NASA NTRS1975

Scanning Kirkpatrick-Baez X-ray telescope to maximize effective area and eliminate spurious images - Design

We consider the design of a Kirkpatrick-Baez grazing-incidence X-ray telescope to be used in a scan of the sky and analyze the distribution of both properly reflected rays and spurious images over the field of view. To obtain maximum effective area over the field of view, it is necessary to increase the spacing between plates for a scanning telescope as compared to a pointing telescope. Spurious images are necessarily present in this type of lens, but they can be eliminated from the field of view by adding properly located baffles or collimators. Results of a computer design are presented.

Kast, J. W.↗
NASA NTRS1975

An experimental investigation of multiple ion processes in mercury bombardment thrusters

Utilizing a collimated E x B mass separator probe, the ratio of double to single ion current densities has been measured in the beam of a 30 cm ion thruster over a wide range of beam and discharge conditions. For a specified thruster geometry, the mass utilization efficiency has been found to be the governing parameter in the determination of the doubly-charged ion content. By a reduction in the open area of the accelerator grid, a reduction in the doubly-charged ion ratio could be achieved while maintaining overall efficiency constant. The results are examined in terms of ion densities and neutral loss rates.

Vahrenkamp, R.↗
NASA NTRS1975

Thresholds for the perception of angular acceleration as indicated by the oculogyral illusion

A motorized chair (with precise servo controls) accelerated the observer in a clockwise (CW) or counterclockwise (CCW) direction at rates that ranged in logarithmic progression from 0.02 to 6.00 deg/sq sec. The target, a narrow collimated line of light, was contained within a goggle device worn by the observer and therefore fixed in relative position to him. The illusion, appearing as rightward or leftward movement of the visual target in the direction of acceleration, was determined by a double staircase procedure among 300 normal and 4 labyrinthine-defective observers. None of the latter perceived the illusion. The majority of normal observers revealed no substantial directional difference (CW vs. CCW threshold). Threshold frequency distributions ranged in rate (deg/sq sec) from 0.020 to 0.950; the threshold of response in more than half the normal observers was less than 0.10, in over three-fourths was less than 0.20, in over 90% less than 0.30, and 100% less than 1.00.

Miller, E. F., II↗
NASA NTRS1975

Operational performance of a low cost, air mass 2 solar simulator

The present work describes briefly the design, construction, and operation of a low cost air mass 2 solar simulator, and then presents the performance characteristics of a modified version in terms of total irradiance, uniformity of irradiance, spectral distribution, and beam subtense angle. The simulator consists of an array of 143 tungsten halogen lamps and a corresponding array of 143 Fresnel lenses parallel and in front of the lenses, so that a 1.2 m by 1.2 m area is irradiated with uniform collimated irradiance. The performance of this 143-lamp version is compared with that of the 12-lamp prototype. It was found that the larger design required a lower lamp voltage for an equivalent average total irradiance in the test plane. However, distribution of total irradiance was not as good for the large simulator.

Yass, K.↗
NASA NTRS1975

Auroral zone microbursts, substructures, and a model for microburst precipitation

The spatial and temporal characteristics of X-ray microbursts detected by collimated directional telescopes have been analyzed in detail. Results indicate the presence of a persistent periodicity of about 0.5 second and 1.2 seconds, respectively. In one event, microbursts exhibit fine structures similar to those observed by Lampton (1967). These substructures are poorly correlated in both space and time as indicated by the low correlation coefficients obtained in auto- and cross-correlation analyses between various pairs of telescopes. The source dimension of these substructures is deduced to be less than 18 km at ionospheric heights. By considering that microburst electrons are near regions of strong diffusion, we show that microburst precipitation can be generated if electric field turbulence is present in the magnetosphere. We argue that electrons of about 50 keV in bounce resonance with a parallel electric field of about 1 millivolt/meter at about 1 Hz can account for the microburst period as well as the precipitation lifetime of about 0.2 second.

Parks, G. K.↗
NASA NTRS1975

Crab Nebula observations - 0.2-10 MeV

Observations of the total emission from the Crab Nebula and also of the pulsed component were made over the 0.2 to 10-MeV range during three balloon flights in 1971 with an actively-collimated NaI scintillator. The total emission flux was positively observed over the entire interval. The observed spectrum to 1 MeV agrees with an extrapolation of the E to the -2.2 power law, which fits lower-energy data. The observations above 1 MeV are factors of 3 and 20 above this law and are better fit with a spectral index of 0.8. Confidence levels are 3 sigma or better for each half-decade band. The three observations are consistent with a constant flux level. The NP 0532 flux, detected during one flight only (August 8) between 0.2 and 0.38 MeV, agrees with the exponential power law spectrum already determined from other observations. The possibility of a rapidly rising pulsed emission fraction over the 0.1- to 1-MeV interval is excluded by this observation.

Gruber, D. E.↗
NASA NTRS1975

The X-ray line and continuum emission from a solar active region

The X-ray spectrum of the quiet sun in the energy range of 2.3-6.9 keV was observed from an Aerobee rocket using an uncollimated graphite crystal spectrometer. These results and spatial measurements made with an onboard modulation collimator are analyzed using solar models. Several methods of estimating coronal temperatures are used in the analysis and all yield results within the range of (4 plus or minus 1) million K.

Landecker, P. B.↗
NASA NTRS1976

Contrast enhancement of transparencies

System can enhance or reduce contrast of photographic transparency for printing or projection by using constructive and destructive interference of collimated laser beam. System is potentially less expensive than electronic CRT methods and is more accurate than trial-and-error manual techniques.

Shulman, A. R.↗
NASA NTRS1975

Quantitative determination of smoke and toxic product potential of materials with the AMINCO (registered) NBS smoke density chamber

Quantitative measurements of smoke obscuration produced by standard area samples under high energy pyrolysis both with and without an ignition source, using a collimated vertical light beam in conjunction with an ultra-linear photomultiplier microphotometer are obtainable with the smoke density chamber. Results are expressed in dimensionless specific optical density permitting usage calculations in accordance with a geometric relationship.

Greenberg, S.↗
NASA NTRS1975

Mapping X-ray heliometer for Orbiting Solar Observatory-8

An instrument combining mechanical collimators and proportional counter detectors was designed to record solar X-rays with energies of 2-30 keV with good temperal, spectral, and spatial resolution. The overall operation of the instrument is described to the degree needed by personnel who interact with the experimenter during SC/experiment interfacing, experiment testing, observatory integration and testing, and pre/post launch data processing. The general layout of the instrument is given along with a summary of the instrument characteristics.

Acton, L. W.↗
NASA NTRS1976

Test plane uniformity analysis for the MSFC solar simulator lamp array

A preliminary analysis was made on the solar simulator lamp array. It is an array of 405 tungsten halogen lamps with Fresnel lenses to achieve the required spectral distribution and collimation. A computer program was developed to analyze lamp array performance at the test plane. Measurements were made on individual lamp lens combinations to obtain data for the computer analysis. The analysis indicated that the performance of the lamp array was about as expected, except for a need to position the test plane within 2.7 m of the lamp array to achieve the desired 7 percent uniformity of illumination tolerance.

Griner, D. B.↗
NASA NTRS1975

Sketch of a unifying auroral theory

On the basis of field and particle observations, it is suggested that a bright auroral display is a part of a magnetosphere-ionosphere current system which is fed by a charge-separation process in the outer magnetosphere (or the solar wind). The upward magnetic-field-aligned current is flowing out of the display, carried mainly by down-flowing electrons from the hot-particle populations in the outer magnetosphere (the ambient cold electrons being depleted at high altitudes). As a result of the magnetic mirroring of these downflowing current carriers, a large potential drop is set up along the magnetic field, increasing both the number flux and the kinetic energy of the precipitating electrons. It is found that this simple basic model, when combined with wave-particle interactions, may be able to explain a highly diversified selection of auroral particle observations. It may thus be possible to explain both inverted-V events and auroral rays in terms of a static parallel electric field, and the electric field may be compatible with a strongly variable pitch-angle distribution of the precipitating electrons, including distributions peaked at 90 deg as well as 0 deg. This model may also provide a simple explanation of the simultaneous precipitation of electrons and collimated positive ions.

Lennartsson, W.↗
NASA NTRS1976

Pulsed X-ray observations of Cen X-3 from Ariel-5

The 4.8 second X-ray pulsations from Centaurus X-3 were monitored by the MSSL collimated proportional counter on board Ariel-5 between 18-27 January 1975. Analysis of the source Doppler effect shows that the pulsation period of Cen X-3 decreased by 3.70 + or - 0.04 milliseconds during the preceding 2.3 years. The Doppler analysis also yields updated values for the binary phase and period of Cen X-3. Phase zero occurred at JD 2442438.628 + or - 0.003, and the average heliocentric binary period between October 1972 and January 1975 was 2.087129 + or - 0.000007 days. Light curves of the 4.8 second pulsations in the 3-9 keV band are characterized by two pronounced peaks, in contrast with the single peak profiles observed by Uhuru.

Tuohy, I. R.↗
NASA NTRS1976

Observations of A0620-00 by SAS-3

The transient X-ray source A0620-00 was observed by the SAS-3 group with the SAS-3 X-ray observatory. At maximum X-ray luminosity limits of 2% were placed on periodic variations from 0.2 ms - 2,000 sec. A precise position was obtained with the rotating modulation collimator. This led directly to radio and optical identification by groups at the NRAO, Arecibo, and McGraw Hill Observatories. The low energy (0.15-0.9 keV) system was pointed at the source, and a spectrum was derived. Hardness ratios are presented, as well as detailed light curves.

Bradt, H.↗
NASA NTRS1976

An estimate of the influence of sediment concentration and type on remote sensing penetration depth for various coastal waters

Under the assumptions of collimated light, a homogenous water column, zero molecular scattering, and constant ratio of volume scattering function to scattering coefficient, estimates of the remote sensing depth parameter, Z90, are made for various coastal waters at 540 nm. Calculations indicate that sediment concentration and type have a strong influence on remote sensing depth when concentrations are below 5 mg/theta. Above 5 mg/theta, the absorption coefficient of the sediments becomes large in comparison to that of water, causing Z90 values to be less than 2 m with only small differences between various sediment types.

Whitlock, C. H.↗
NASA NTRS1976

Apollo 16 far-ultraviolet imagery and spectra of the Large Magellanic Cloud

The Large Magellanic Cloud was observed by the far ultraviolet camera spectrograph from the lunar surface during the Apollo 16 mission 22 April 1972. Images were obtained with about 3 arc min resolution, in the 1,050 to 1,600 and 1,250 to 1,600 A wavelength ranges, of nearly the entire LMC. Spectra were also obtained in the 1,050 to 1,600 and 900 to 1,600 A ranges along a strip 1/4 deg wide (determined by the instrument's grid collimator) passing across the LMC. The images and spectra have been scanned with a PDS microdensitometer, and isodensity contour plots have been prepared using the Univac 1108 computer.

Page, T.↗
NASA NTRS1975

Instrumental technique in X-ray astronomy

A detailed review of the development of instruments for X-ray astronomy is given with major emphasis on nonfocusing high-sensitivity counter techniques used to detect cosmic photons in the energy range between 0.20 and 300 keV. The present status of X-ray astronomy is summarized together with significant results of the Uhuru observations, and photon interactions of importance for the detection of X-rays in space are noted. The three principal devices used in X-ray astronomy (proportional, scintillation, and solid-state counters) are described in detail, data-processing systems for these devices are briefly discussed, and the statistics of nuclear counting as applied to X-ray astronomy is outlined analytically. Effects of the near-earth X-ray environment and atmospheric gamma-ray production on X-ray detection by low-orbit satellites are considered. Several contemporary instruments are described (proportional-counter systems, scintillation-counter telescopes, modulation collimators), and X-ray astronomical satellite missions are tabulated.

Peterson, L. E.↗