SEARCH · Engineering Papers
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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Selected fire-retardant materials for possible application to commercial aircraft are described. The results of flammability screening tests and information on the physical and chemical properties of both original and newly installed materials after extended use are presented in tabular form, with emphasis on wear properties, strength, puncture and tear resistances, and cleanability.
Photometry and polarimetry of the cometary heads one of the most important sources of information about the physical processes in comets is reviewed. Methods of inspection discussed include: narrow band photometry, wide band photometry, color photography, tilting filter techniques, and photoelectric spectrum scanning. Results of photoelectric observations of comets are described including photoelectric and infrared measurements of comet Kohoutek. Photometric profiles of the coma in monochromatic light are used to determine the lifetime of the parent molecules for the observed radicals, CN and C2.
A basic model and simple numerical relations useful for future far infrared studies of the galaxy are presented. Making use of recent CO and other galactic surveys, the diffuse far infrared flux distribution from the galactic plane as a function of galactic longitude alternate theta for 4 deg or = alternate theta or = 90 and the far infrared emissivity as a function of galactocentric distance is predicted. Future measurements of the galactic far infrared flux would yield valuable information on the physical properties and distribution of dust and molecular clouds in the galaxy, particularly the inner region.
Information regarding the physical characteristics of Titan and atmospheric models necessary to support design and mission planning of spacecraft that are to orbit Titan, enter its atmosphere or land on its surface is given.
The paper reviews the observations of solar X-rays in the range 1-100 keV made by the solar X-ray instrument on board the OSO-7 satellite and explores the relationship between the hard and soft X-ray components in order to glean some information on the physics of solar flares. Some of the results are as follows: The growth of the soft X-ray emission in a burst must be due to the addition of new hot material to the flare plasma. The anticorrelation between cooling time and maximum plasma temperature gives new evidence to support conduction as the principal cooling mechanism of the hot flare plasma. Observations of hard X-ray emission from bursts which occurred behind the limb indicate that hard X-ray emission comes at least in part from considerable heights in the corona.
Results are presented on the direct observations of the circumstellar shell around alpha-Ori, along with new observations of the Ca II infrared triplet lines which provide lower limits for the Ca(+) shell radii for alpha-Ori and alpha-Sco (Antares). The 8542-A line in alpha-Ori does not show a circumstellar absorption core, and the shell radius limit is estimated to be at least 31 times stellar radius. A 108-mA circumstellar core is observed in the 8542-A line in Antares for which a shell radius equal to 4.0 times stellar radius is suggested. The discovery of circumstellar emission through resonance line scattering will provide valuable additional information on the physical conditions in the shell.
A basic model and simple numerical relations useful for future far-infrared studies of the Galaxy are presented. Making use of recent CO and other galactic surveys, the diffuse far-infrared flux distribution from the galactic plane is predicted as a function of galactic longitude for longitudes between 4 and 90 deg; the far-infrared emissivity is predicted as a function of galactocentric distance. Future measurements of the galactic far-infrared flux would yield valuable information on the physical properties and distribution of dust and molecular clouds in the Galaxy, particularly the inner region.
A basic model and simple numerical relations useful for future far-infrared studies of the Galaxy are presented. Making use of recent CO and other galactic surveys, the diffuse far-infrared flux distribution from the galactic planes is predicted as a function of galactic longitude for the region between 4 and 90 deg longitude; the far-infrared emissivity is predicted as a function of galactocentric distance. Future measurements of the galactic far-infrared flux would yield valuable information on the physical properties and distribution of dust and molecular clouds in the Galaxy, particularly the inner region.
Current status, projected goals, and results of 49 research and advanced development programs at the Jet Propulsion Laboratory are reported in abstract form. Areas of investigation include: aerodynamics and fluid mechanics, applied mathematics and computer sciences, environment protection, materials science, propulsion, electric and solar power, guidance and navigation, communication and information sciences, general physics, and chemistry.
The paper examines methods of analyzing and interpreting solar X-ray photographs obtained by soft X-ray telescopes such as those used during the Skylab mission, to obtain information on the physical conditions that give rise to coronal X-ray emitting features revealed by inspection or microdensitometry of the X-ray photographs. First, the differential emission measure function is defined. By choosing models for this function and calculating the integral for the irradiance at the film for each filter, one calculates the effective temperature and emission measure. This method gives correct results only when applied to isothermal regions. For heterothermal regions, a modeling approach which predicts the run of temperature and density, and thus the form of the differential measure function, is used.
Questions of the importance and feasibility of performing experiments on droplet burning at zero gravity in Spacelab were studied. Information on the physics and chemistry of droplet combustion, with attention directed specifically to the chemical kinetics, heat and mass transfer, and fluid mechanics of the phenomena involved, are presented. The work was divided into three phases, the justification, the feasibility, and the conceptual development of a preliminary design. Results from the experiments performed revealed a few new facts concerning droplet burning, notably burning rates in excess of theoretical prediction and a phenomenon of flash extinction, both likely traceable to accumulation of carbon produced by gas-phase pyrolysis in the fuel-rich zone enclosed by the reaction surface. These experiments also showed that they were primarily due to timing difficulties.
Ultraviolet observations of the extended atmospheres and circumstellar envelopes of early-type and cool stars are reviewed. UV spectra of OB stars have shown that mass loss occurs in virtually all these stars and in many Be stars, and the Copernicus satellite has also provided information on the physical conditions and variability of the winds. The winds have been interpreted in terms of hot coronal wind models, imperfect flow models and radiation pressure models, and estimates of mass loss ranging from 10 to the -10th to 9 x 10 to the -6th solar masses/year have been obtained. Further UV data of faint stars, additional wavelengths and time variability are required. Recent UV and X-ray experiments have detected stellar chromospheres, transition regions coronas and winds in cool stars. Semiempirical line-profile and line-flux models and purely theoretical atmospheric models have been constructed to explain chromosphere, corona and wind data, and future observations of the physical properties of stellar chromospheres, coronas and winds, terms in the energy balance equation, stellar activity and its long-term variability and atmospheric modifications due to the presence of companion stars are proposed for such missions as Spacelab.
The purpose of this paper is to report the preliminary findings of hydrogen vapor cloud dispersion experiments conducted by NASA. The experiments were performed to obtain basic information regarding the physical phenomena governing the dispersion of flammable clouds formed as the result of spills of large quantities of liquid hydrogen. The experiments consisted of ground spills of up to 5.7 cubic meters (1500 gal) of liquid hydrogen, with spill durations of approximately 35 seconds. Instrumented towers, located downwind of the spill site, gather data on the temperature, hydrogen concentration, and turbulence levels as the hydrogen vapor cloud drifted downwind. Visual phenomena were recorded by motion picture and still cameras. Preliminary results of the experiments indicate that, for rapid spills, thermal and momentum induced turbulences cause the cloud to disperse to safe concentration levels and become positively buoyant long before mixing due to normal atmospheric turbulence becomes a major factor.
The first order Fermi acceleration mechanism of cosmic rays in shocks may be at work for neutrinos in supernova shocks when the latter are at densities greater than 10 to the 13th g/cu cm, at which the core material is opaque to neutrinos. A Monte Carlo approach to study this effect is employed, and the emerging neutrino power law spectra are presented. The increased energy acquired by the neutrinos may facilitate their detection in supernova explosions and provide information about the physics of collapse.
It is thought likely that the study of spectral lines in the far-infrared might provide at least as much information about the physics and chemistry of the interstellar environment as radioastronomy. However, by comparison with the microwave region, the far-infrared is largely unexplored. There is a pressing need for good laboratory data to aid searches and assignments of spectra from the interstellar clouds and nebulae. Brown et al. (1981) have conducted a study of the laser magnetic resonance (LMR) spectrum of the OH radical in its ground state at far-infrared wavelengths. The present investigation is concerned with the computation of the frequencies of individual hyperfine transitions involving all rotational levels up to J = 4 1/2. The results of the calculation are presented in a table. The results are summarized in a diagram which shows the low-lying energy levels of OH. The frequencies of transitions between levels studied directly in the LMR spectrum are quite reliable.
Recent advances in determining the elemental, charge state, and isotopic composition of or approximate to 1 to or approximate to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations. Average values of relative abundances measured in a large number of SEP events were found to be roughly energy independent in the approx. 1 to approx. 20 MeV per nucleon range, and showed a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion. Direct measurements of the charge states of SEPs revealed the surprisingly common presence of energetic He(+) along with heavy ion with typically coronal ionization states. High resolution measurements of isotopic abundance ratios in a small number of SEP events showed these to be consistent with the universal composition except for the puzzling overabundance of the SEP(22)Ne/(20)Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of (3)He rich, heavy ion rich and carbon poor SEP events, along with direct measurements of the ionization states of SEPs provided essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production.
A theoretical model developed to calculate pressure-temperature cross spectra, pressure spectra, temperature spectra and pressure cross spectra in a ducted combustion system is presented. The model assumes the presence of a fluctuating-volumetric-heat-release-rate disk source and takes into account the spatial distribution of the steady-state volumetric-heat flux. Using the model, pressure, velocity, and temperature perturbation relationships can be obtained. The theoretical results show that, at a given air mass flow rate, the calculated pressure-temperature cross spectra phase angle at the combustor exit depends on the model selected for the steady-state volumetric-heat flux in the combustor. Using measurements of the phase angle, an appropriate source region model was selected. The model calculations are compared with the data. The comparison shows good agreement and indicates that with the use of this model the pressure-temperature cross spectra measurements provide useful information on the physical mechanisms active at the combustion noise source.
The spectra of the Orion KL molecular cloud and the envelope of the carbon star IRC+10216 are surveyed at 1 MHz resolution over the interval 72.2-91.1 GHz to a sensitivity usually better than 0.1 K. Multitransition analysis of several molecular species is presented which gives information on the physical conditions and chemical abundance in the Orion KL region. The excitation conditions and relative abundances in the IRC+10216 envelope are surveyed. It is stressed that the low detection rate of molecular lines in this object does not necessarily imply a poorer chemistry compared with that in interstellar clouds, but is partly a reflection of low abundances and unsatisfied excitation requirements.