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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Radio and X-ray variability of the nucleus of Centaurus A (NGC 5128)

Centaurus A was observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons.

Beall, J. H.↗
NASA NTRS1978

Cometary brightness variation and nucleus structure

The Bobrovnikoff and Beyer photometric data for more than 100 comets analyzed for intrinsic brightness variations, before and after perihelion, according to some inverse power law of solar distance. The Oort and Schmidt classification of comet age is extended and applied with Marsden's new determinations of inverse semimajor axis. A physical interpretation of the data involves the quick loss of a frosting of supervolatile materials from new comets, and for all comets, the development of an insulating crust after perihelion. The orientation of the axes of rotating comets is shown to be an important factor in cometary brightness variations. A speculation is made concerning the axis of rotation of Comet Kohoutek.

Whipple, F. L.↗
NASA NTRS1979

Atomic electron excitation probabilities during orbital electron capture by the nucleus

Approximate probabilities of electron excitation (shakeup/shakeoff) from various atomic states during nuclear ns electron capture have been calculated in the sudden approximation, using Hartree-Fock wave functions. Total excitation probabilities are much lower than during inner-shell ionization by photons or electrons, and ns states are more likely to be excited than np states. This latter result is borne out by K-alpha X-ray satellite spectra.

Crasemann, B.↗
NASA NTRS1980

Ice nucleus concentrations measured during the 1975 Florida Area Cumulus Experiment /FACE/

Ice nuclei measurements were made aboard a cloud-base aircraft during the 1975 Florida Area Cumulus Experiment. Two techniques were used to obtain the ice nuclei concentrations; membranes were collected and analyzed using the NCAR membrane development chamber and continuous ice nuclei concentrations were obtained using the NCAR acoustical counter. Results showed that the membrane technique failed to effectively detect ice nuclei in this maritime tropical area. However, the concentrations recorded by the acoustical counter showed natural afternoon diurnal increases which may have ramifications on cloud development and seeding potential within the particular study area.

Wisniewski, J.↗
NASA NTRS1976

Cometary nucleus release experiments and ice physics

Some physical and chemical processes involved in the evaporation and sublimation of mixtures of frozen gases are discussed. Effects of zero gravity, vacuum, and solar radiation are emphasized. Relevant experiments that can be carried out with the aid of the space shuttle are proposed.

Huebner, W. F.↗
NASA NTRS1981

Observations of the nucleus of M100

The galaxy M100 = NGC 4321 is a spiral galaxy in which a bright Type II Supernova was discovered on April 19, 1979. Its spectral evolution was followed with IUE for more than two months (refs. 1,2). At all epochs, the spectrum was dominated by continuous radiation on which emission and absorption features were superimposed. The equivalent width of most of the absorption features appeared not to vary with time suggesting that they originated in the interstellar media of M100 and our own galaxy.

Panagia, N.↗
NASA NTRS1981

VLBI observations of the nucleus of the radio galaxy Cygnus A

The central component of the radio galaxy Cygnus A has been observed in several (very long baseline interferometry) experiments between 1975 and 1979, and the results have been combined to derive a model for the brightness distribution. Some 65% of the nuclear emission appears to come from a compact core. The remaining flux density comes from a more extended region (or regions) up to 4 or 5 mas away lying along a position angle near 100 deg, which is close to that of the extended lobes. Evidence that compact central components reflect the collimation and transport of energy to the outer lobes of radio galaxies is discussed, and several interpretations of the observed asymmetries are considered.

Kellermann, K. I.↗
NASA NTRS1981

A cloud condensation nucleus spectrometer designed for airborne measurements

The spectrometer is a simple extension of the continuous flow diffusion chamber (CFDC) operated in the vertical mode. The principal new design features of the instrument are its rapid time response and ability to rapidly measure the CCN activity spectrum. The activity spectrum of CCN in an air sample is measured by simultaneously operating the spectrometer at four supersaturations. The CCN spectrometer consists of four essentially indepenent CFDC's in a parallel array. Each CFDC is 61 cm long, 10 cm wide, and consists of two vertical parallel plates 1 cm apart, maintained at different temperatures. Each CFDC has a single particle optical counter located at the center of its base.

Radke, L. F.↗
NASA NTRS1981

Cloud condensation nucleus counter by impactor sampling technique

Unlike typical CCN counters, this device counts the numbers of water droplets condensed on aerosol particles sampled on a microcover glass at various different relative humidities. The relative humidities ranged from 75 percent to a calculated value of 110 percent. A schematic of the apparatus is shown. The individual CCN can be identified in an optical micrograph and scanning electron micrograph and may be inspected for their chemical composition later.

Ohtake, T.↗
NASA NTRS1984

The friable sponge model of a cometary nucleus

The mantle/core model of cometary nuclei, first suggested by Whipple and subsequently developed by Mendis and Brin, is modified and extended. New terms are added to the heat conduction equation for the mantle, which is solved in order to obtain the temperature distribution in the mantle and the gas production rate as a function of mantle thickness and heliocentric distance. These results are then combined with some specific assumptions about the mantle structure (the friable sponge model) in order to make predictions for the variation of gas production rate and mantle thickness as functions of heliocentric distance for different comets. A solution of the time-dependent heat conduction equation is presented in order to check some of the assumptions.

Horanyi, M.↗