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NASA NTRS1981

Radio and visible light observations of matter ejected from the sun

An initial set of visible light and radio observations of a coronal transient made with the Coronagraph/Polarimeter experiment on SMM and the radioheliograph at Culgoora, Australia is presented. It is noted that an enormous loop-shaped transient observed on April 7, 1980, exhibited bright material having whiplike, nonradial motions, as well as moving and stationary radio sources. The data make it possible to establish that a moving type IV radio source was located on or very close to the fast-moving loop. The thermal, kinetic, and magnetic energies in the transient are estimated and, for the first time, compared with the radiative energy of the associated flare.

Wagner, W. J.↗
NASA NTRS1981

Global atmospheric distribution and trend of methylchloroform /CH3CCl3/

Results of global measurements of the concentration of atmospheric methylchloroform, a man-made gas with potentially harmful environmental consequences, performed over a two-year period are presented. Samples were collected weekly at Pt. Barrow and Poker Flats, Alaska, Cape Meares, Oregon, Cape Kumakahi, Hawaii, Samoa, and Cape Grim, Tasmania, and yearly at the South Pole, and methylchloroform concentrations were determined by electron capture-gas chromatographic techniques. A latitudinal profile of CH3CCl3 concentrations derived from the data exhibits a bump at high northern latitudes, where most of the sources are located. Average concentrations calculated for the Northern and Southern Hemispheres showed a rise in global concentrations at a rate of 6.7 + or - 2.0%/year for the period from January 1979 to January 1981, with concentrations rising more slowly in 1980 than in 1979. These yearly increases are also smaller than earlier rates of increase, explainable by a reduction in the rate of emission increase, and are consistent with an atmospheric lifetime of between 6 and 10 years.

Rasmussen, R. A.↗
NASA NTRS1981

The energetics of molecular clouds. IV - The S88 molecular cloud

The S88 molecular cloud has been observed in several molecular lines and at infrared wavelengths from 1 to 100 microns. The CO emission has a single, sharp peak which is near the H-alpha emission region S88 B and centered on a compact H II region observed in the radio continuum. The infrared observations indicate that the principal luminosity source is located near the radio continuum peak and is hidden behind substantial extinction, presumably from the molecular cloud. The molecular cloud has a size of about 6.5 pc and a mass of about 5,000 solar masses at an assumed distance of 2 kpc. Regions of very high density (more than 10,000/cu cm) do not seem to be present. Analysis of the energetics leads to a predicted dust cooling rate in good agreement with the infrared observations, which indicate L = 180,000 solar luminosities. A more detailed examination of the energetics indicates that densities may be insufficient for collisions of molecules with warm dust grains to heat the gas to the observed kinetic temperature.

Evans, N. J., II↗
NASA NTRS1982

Discovery of 69 ms periodic X-ray pulsations in A0538-66

The detection of X ray pulsations with a period of 69.2126 ms from A0538-66 was done from the Einstein Observatory. A point source was located by the High Resolution Imager and a proportional counter registered a flux of 40 counts/sec over background. A column spectral density of 2 x 10 to the 23/sq cm identified the object as A0538-66. A persistent periodicity of 0.0692126 sec was observed throughout the event. The outbursts were not detected on three other observations of A0538-66, and a best fit to a change of rotation velocity indicated that the period observed was from a binary star with a Doppler shifted signal. The two stars are separated by less than 39 solar radii, with the larger star having a 40 solar radius. Consideration is given to the possibility that the X rays are due to accretion on a neutron star and that the two stars at times share a common envelope.

Skinner, G. K.↗
NASA NTRS1984

High-Resolution X-Ray Telescope

X-ray telescope for mapping celestial X-ray sources from locations in space uses secondary mirror to magnify images formed by primary mirror. Secondary mirror with hyperboloid/hyperboloid surface located at focal plane of primary mirror.

Davis, J. M.↗
NASA NTRS1982

On the structure of an underexpanded rectangular jet

An underexpanded jet of air issuing from a converging rectangular nozzle of moderate aspect ratio was investigated. Schileren pictures of the flow field along with hot-wire measurements in the jet were obtained at different pressure ratios. At the pressure ratio corresponding to the maximum screeching sound, Schlieren photographs show a very strong organized cylindrical wave pattern on either side of the jet, with their respective sources being located at the end of the third shock cell. Associated with this wave pattern is a large increase in the angle of spread of the jet. It is shown that the self excitation helps to induce large-scale vortical motions in the jet both in the plane containing the small dimension of the nozzle and in the plane containing the long dimension of the nozzle. However, the locations of these structures are different in the two planes. Nevertheless, the characteristic Strouhal number corresponding to these large-scale structures in both planes is the same and equal to 0.12. The influence of the self excitation on the mean velocities and rms intensities was also investigated. For the full range of pressure ratios studied, similarity was found in the mean velocity and rms intensity profiles in the two central planes beyond 80 widths downstream of the nozzle exit. However, the shapes of the similarity profiles are different in the two planes.

Krothapalli, A.↗
NASA NTRS1982

Volcanic eruption plumes on Io

The nine eruption plumes observed by Voyager 1 are discussed. The plumes range in height from about 60 to over 300 km with corresponding ejection velocities of about 0.5 to 1.0 km/s. Plume sources are located on level plains rather than topographic highs and consist of either fissures or calderas. Except for Ple, the brightness distribution monotonically decreases from the core to the top of the plume. Numerous surface deposits similar to those associated with active plumes probably mark the sites of recent eruptions. The distribution of active and recent eruptions appears to be concentrated in the equatorial regions. This suggests that the depositional rate is greater and the surface age younger in the equatorial regions, possibly accounting for the active eruptions suggests that sulfur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes.

Strom, R. G.↗
NASA NTRS1983

Association between gradual hard X-ray emission and metric continua during large flares

X-ray radiation is used to study coronal phenomena in conjunction with meter wave observations during some large solar flares. It is found that metric flare continua and moving type IV bursts are associated with gradual and long lasting (a few tens of minutes) microwave and hard X-ray emissions. The detailed temporal analysis reveals that although metric and hard X-ray sources are located at very different heights, both kinds of emission result from a common and continuous/repetitive injection of electrons in the corona. The late part of the metric event (stationary type IV burst) is only associated with soft X-ray radiation. This indicates that the mean energy of the radiating electrons is lower during stationary type IV bursts than during the earlier parts of the event.

Klein, L.↗
NASA NTRS1983

EGRET - The high energy gamma ray telescope for NASA's Gamma Ray Observatory

The EGRET high energy gamma-ray telescope under development for NASA's Gamma Ray Observatory will have an energy range of approximately 12 to 30,000 MeV, energy resolution of about 15 percent FWHM over most of that range, an effective area of about 2000 sq cm at high energies, and single photon angular accuracy of approximately 2 deg at 100 MeV, less than 0.1 deg above 5 GeV. This instrument can locate strong sources to an accuracy of about 5 arc min. The instrument utilizes a set of digital spark chambers interleaved with tantalum foils for detection and identification of gamma-ray events, and a large NaI(Tl) scintillator for energy determination. The system is triggered by a coincidence matrix using two arrays of plastic scintillation counters and a large plastic scintillator anticoincidence dome that rejects incident charged particles.

Fichtel, C. E.↗
NASA NTRS1985

Correlation of solar decimetric radio bursts with X-ray flares

Several hundred radio bursts in the decimetric wavelength range (300-1000 MHz) have been compared with simultaneous soft and hard X-ray (HXR) emission. Long lasting (type IV) radio events have been excluded. The association of decimetric emission with hard X-rays has been found to be surprisingly high (48 percent). The association rate increases with bandwidth, duration, number of structural elements, and maximum frequency. Type III-like bursts are observed up to the upper limit of the observed band. This demonstrates that the corona is transparent up to densities of about 10 to the 10th/cu cm, contrary to previous assumptions. This can only be explained in an inhomogeneous corona with the radio source being located in a dense structure. The short decimetric bursts generally occur during the impulsive phase, i.e., simultaneously with hard X-rays. The times of maximum flux are well correlated (within 2 s). The HXR emission lasts 4 times longer than the radio emission in the average. This work finds a close relationship between decimetric and HXR emission, with sufficient statistics offering additional information on the flare process.

Aschwanden, M. J.↗
NASA NTRS1984

The dissociation of subjective measures of mental workload and performance

Dissociation between performance and subjective workload measures was investigated in the theoretical framework of the multiple resources model. Subjective measures do not preserve the vector characteristics in the multidimensional space described by the model. A theory of dissociation was proposed to locate the sources that may produce dissociation between the two workload measures. According to the theory, performance is affected by every aspect of processing whereas subjective workload is sensitive to the amount of aggregate resource investment and is dominated by the demands on the perceptual/central resources. The proposed theory was tested in three experiments. Results showed that performance improved but subjective workload was elevated with an increasing amount of resource investment. Furthermore, subjective workload was not as sensitive as was performance to differences in the amount of resource competition between two tasks. The demand on perceptual/central resources was found to be the most salient component of subjective workload. Dissociation occurred when the demand on this component was increased by the number of concurrent tasks or by the number of display elements. However, demands on response resources were weighted in subjective introspection as much as demands on perceptual/central resources. The implications of these results for workload practitioners are described.

Yeh, Y. H.↗
NASA NTRS1985

Coronal temperatures, heating, and energy flow in a polar region of the sun at solar maximum

The profiles of resonantly scattered Lyman-alpha coronal radiation have been used to determine the hydrogen kinetic temperature from 1.5 to 4 solar radius from the center of the polar region of the corona observed in 1980 at solar maximum. Hydrogen temperatures derived from the line profiles were found to decrease with height from 1.2 million K at r = 1.5 solar radii to 600,000 K at r = 4 solar radius. Comparison of the measured kinetic temperatures with predictions from a semiempirical two-fluid model showed evidence of a small amount of heating or a nonthermal contribution to the motions of coronal protons between 1.5 and 4 solar radius. The widths of the profiles confirmed an upper limit of 110 + or - 15 km/s on the rms magnitude of the line-of-sight component of velocities between 1.5 and 4 solar radius. Density measurements obtained in situ in the solar wind in the ecliptic were used to locate the sources of low speed and high-speed winds in the polar region. An eclipse photograph of the corona at solar maximum is provided.

Withbroe, G. L.↗
NASA NTRS1985

Using the ET for gamma-ray astronomy

A gamma-ray-telescope design is presented which makes use of the normally spent external tank (ET) of the Space Shuttle as the spacecraft and Cerenkov pressure vessel. The ET would be configured into the telescope once onorbit, using the Space Station as the base of operations for carrying out the assembly activities. The telescope provides a continuation to the NASA program in high-energy astrophysics, providing for follow-on observations to the survey work of the EGRET instrument on GRO. The most important features of the gamma-ray imaging telescope system are its collecting area of 250,000 sq cm per ET (40 times that of the EGRET instrument) and its ability to locate point sources to within several arc minutes.

Koch, D.↗
NASA NTRS1986

The evolution of methods for noise prediction of high speed rotors and propellers in the time domain

Linear wave equation models which have been used over the years at NASA Langley for describing noise emissions from high speed rotating blades are summarized. The noise sources are assumed to lie on a moving surface, and analysis of the situation has been based on the Ffowcs Williams-Hawkings (FW-H) equation. Although the equation accounts for two surface and one volume source, the NASA analyses have considered only the surface terms. Several variations on the FW-H model are delineated for various types of applications, noting the computational benefits of removing the frequency dependence of the calculations. Formulations are also provided for compact and noncompact sources, and features of Long's subsonic integral equation and Farassat's high speed integral equation are discussed. The selection of subsonic or high speed models is dependent on the Mach number of the blade surface where the source is located.

Farassat, F.↗
NASA NTRS1988

Acoustically excited heated jets. 2: In search of a better understanding

The second part of a three-part report on the effects of acoustic excitation on jet mixing includes the results of an experimental investigation directed at resolving the question of poor excitability of some of the heated jets. The theoretical predictions discussed in Part 1 are examined to find explanations for the observed discrepancies between the measured and the predicted results. Additional testing was performed by studying the self excitation of the shock containing hot jets and also by exciting the jet by sound radiated through source tubes located externally around the periphery of the jet. The effects of nozzle-exit boundary layer conditions on jet excitability was also investigated. It is concluded that high-speed, heated jet mixing rates and consequently also the jet excitability strongly depends on nozzle exit boundary layer conditions.

Lepicovsky, J.↗
NASA NTRS1987

G0.18-0.04 - Interaction of thermal and nonthermal radio structures in the arc near the galactic center

Using a high-resolution radio-continuum image made at a frequency of 4.8 GHz, the radio source G0.18-0.04 located at the intersection of the galactic center Arc with the galactic plane is discussed. In this direction, the radio Arc is composed of a set of linear, nonthermal filamentary structures superimposed on a narrow, sickle-shaped, thermal feature which crosses them. The radio image suggests a physical interaction between the thermal and nonthermal structures. It is argued that the magnetic field is dynamically important and that its strength is estimated to be very large (0.001 G). Furthermore, it is suggested that the ionization of G0.18-0.04 is caused by collisional ionization rather than ultraviolet photons from massive stars. The discussion presents possible ways in which some of the energy of the relativistc particles or the magnetic field in the nonthermal filaments might be extracted to ionize ambient gas in the galactic plane.

Yusef-Zadeh, Farhad↗
NASA NTRS1987

All-sky monitors for X-ray astronomy

The rationale for a semipermanent all-sky X-ray monitor and a variety of options for its implementation are discussed. It is concluded that the Space Station offers an excellent opportunity for hosting such a monitor, and that a set of pinhole cameras can be configured to provide an effective and economical monitor system. A baseline of six independent pinhole modules, each of which requires approximately 1 cu ft, 30 pounds, 2 W and 100 bits per second, can provide full sky coverage with scientifically interesting sensitivities. No other resources or special accommodation (such as detailed alignment registration, time-tagging, or on-orbit servicing) would be required. The baseline system can locate bright sources to a few arcmin and can simultaneously measure each of the several hundred sources in the sky brighter than a few thousandths the intensity of the Crab nebula every day for decades.

Holt, Stephen S.↗
NASA NTRS1987

The main source of radio emission from the magnetosphere of Uranus

Observations of kilometric radiation from Uranus made with the planetary radio astronomy experiment on the Voyager 2 spacecraft are presented and discussed. Similarities between the auroral kilometric radiation from earth and the observed Uranus emission are pointed out. A geometrical beaming model is developed in which a single distributed source is located above the darkside auroral region and emits in the extraordinary mode by the cyclotron maser process. The model can account for nearly all the Uranian kilometric radiation from the high-frequency limit near 850 kHz down to about 150 kHz and for much of it down to the lower limit of 20 kHz.

Gulkis, Samuel↗