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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 1,405 records · Page 78
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NASA NTRS1989

IRAS observations of a large sample of normal irregular galaxies

IRAS 12, 25, 60, and 100 micron data are presented for a sample of Irr galaxies which span a large range in star-formation activity. It is found that the dwarf, giant, and amorphous Irr's generally have similar IR properties. The typical L(IR)/L(H-alpha) ratios of most classes of Irr's, except for many of the luminous blue galaxies, are low compared with those of spiral galaxies and are consistent with the Irr's being relatively transparent systems without large amounts of optically hidden star formation. Compared with spiral galaxies, the Irr's have similar L(IR)/L(B) ratios, warmer S(100)/S(60) ratios, cooler S(25)/S(12) ratios, and lower dust-to-H I gas mass ratios. The temperature, dust-to-H I gas mass ratios, and L(IR)/L(B) ratios do not correlate with the metallicity of the ionized gas of the Irr's. A correlation between the IR fluxes and both the H-alpha and the blue stellar fluxes is found for the Irr's.

Hunter, Deidre A.↗
NASA NTRS1989

The normal modes of a resonant cavity containing discrete inhomogeneities - The influence of fibril magnetic fields on the solar acoustic oscillations

Motivated by considerations of the interaction between fibril magnetic fields and solar p-modes, the acoustic spectrum of a cylindrical cavity filled with ideal gas in which a number of magnetic flux tubes are embedded is studied. A formalism, based on the T-matrix approach to acoustic scattering, is developed which can be used to determine the eigenfrequencies and eigenfunctions for any arbitrary distribution of flux tubes. For weak scatterers, the frequency shifts and velocity eigenfunctions are calculated using perturbation theory for the cases of a single flux tube and a random distribution of up to 100 flux tubes. The results of this 'exact' approach are used to give a critical appraisal of the predictions of theories based on some form of averaging, such as the one discussed recently by Bogdan and Zweibel (1987).

Bogdan, Thomas J.↗
NASA NTRS1990

Local normal galaxies

In the near future, high energy (E greater than 20 MeV) gamma ray astronomy offers the promise of a new means of examining the closest galaxies. Two and possibly three local galaxies, the Small and Large Magellanic Clouds and M31, should be visible to the high energy gamma ray telescope on the Gamma Ray Observatory, and the first should be seen by GAMMA-1. With the assumptions of adequate cosmic ray production and reasonable magnetic field strengths, both of which should likely be satisfied, specific predictions of the gamma ray emission can be made separating the concepts of the galactic and universal nature of cosmic rays. A study of the synchrotron radiation from the Large Magellanic Cloud (LMC) suggests that the cosmic ray density is similar to that in the local region of our galaxy, but not uniform. It is hoped the measurements will be able to verify this independent of assumptions about the magnetic fields in the LMC.

Fichtel, Carl E.↗
NASA NTRS1990

Optical techniques for determination of normal shock position in supersonic flows for aerospace applications

Techniques for the quantitative determination of shock position in supersonic flows using direct and indirect methods is presented. A description of an experimental setup is also presented, different configurations of shock position sensing systems are explained, and some experimental results are given. All of the methods discussed are analyzed to determine the ease of technology transfer from the laboratory to in-flight operation.

Adamovsky, Grigory↗
NASA NTRS1990

An elemental abundance analysis of the superficially normal A star Vega

An elemental abundance analysis of Vega has been performed using high-signal-to-noise 2.4 A/mm Reticon observations of the region 4313-4809 A. Vega is found to be a metal-poor star with a mean underabundance of 0.60 dex. The He/H ratio of 0.03 as derived from He I 4472 A suggests that the superficial helium convection zone has disappeared and that radiative diffusion is producing the photospheric abundance anomalies.

Adelman, Saul J.↗
NASA NTRS1990

The simultaneous integration of many trajectories using nilpotent normal forms

Taylor's formula shows how to approximate a certain class of functions by polynomials. The approximations are arbitrarily good in some neighborhood whenever the function is analytic and they are easy to compute. The main goal is to give an efficient algorithm to approximate a neighborhood of the configuration space of a dynamical system by a nilpotent, explicitly integrable dynamical system. The major areas covered include: an approximating map; the generalized Baker-Campbell-Hausdorff formula; the Picard-Taylor method; the main theorem; simultaneous integration of trajectories; and examples.

Grayson, Matthew A.↗
NASA NTRS1990

Far infrared luminosity functions of normal galaxies

Researchers constructed a volume limited sample of 443 optically selected nearby galaxies from the Zwicky catalog to study far infrared luminosity functions. Schechter function fits and integrated luminosity densities are calculated. Comparing the resulting infrared spectrum with the infrared spectrum for interstellar matter in the solar neighborhood, researchers find most of the infrared emission is due to dust heated by the interstellar radiation field, except at 60 micron emission where star forming regions contribute significantly.

Isobe, Takashi↗
NASA NTRS1991

Heat transfer in rotating serpentine passages with trips normal to the flow

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

Wagner, J. H.↗
NASA NTRS1990

On the tones of round choked jets impinging on normal flat plates

An experimental investigation of the sound produced by an axisymmetric supersonic jet impinging on plates with variable size and nozzle-to-plate spacings was performed. Spectral analysis and schlieren photography were used to determine the sound characteristics and flow disturbances associated with the production of discrete tones. Two classes of tones, associated with small and large plates, existed for pressure ratios above 2.70. For lower pressure ratios, however, only large plate tones occurred for all plate sizes with choked jet screech appearing at the largest spacings. Reflector tests indicated that both classes of tones were part of a feedback loop to the nozzle. Schlieren photography revealed both symmetric and asymmetric disturbances in the large plate jet flows which corresponded to symmetrical and helical modes of oscillation in the cross-spectrum studies. In addition to this, both symmetric and asymmetric oscillations of the shock waves occurred in the large plate case while symmetric oscillations of the shock wave occurred in the small plate case.

Powell, Alan↗
NASA NTRS1990

Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet

The morphology of 218 mid-UV spectra of stars ranging from O through K in spectral type is examined. Several new line and continuum indices are defined and their usefulness as temperature, luminosity, and metallicity discriminants is discussed. Mid-UV stellar continua are found to be markedly affected by abundance. A UV excess, delta(2600-V), is computed which is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B). The relative strength of spectral lines in the mid-UV is not as strongly affected by abundance. Mid-UV spectra are much more sensitive to the temperature of the stellar population than to either metallicity or the dwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying no sensitivity to abundance for cool stars and a reversed sensitivity in FG dwarfs such that metal-poor stars have stronger Mg II strengths at the same temperature than more metal-rich stars.

Fanelli, Michael N.↗
NASA NTRS1990

X-ray emission from normal stars

The paper addresses the potential for future X-ray missions to determine the fundamental cause of stellar X-ray emissions based on available results and existing analyses. The determinants of stellar X-ray emission are listed, and the relation of stellar X-ray emissions to the 'universal' activity-rotation connection is discussed. The specific rotation-activity connection for evolved stars is mentioned, and the 'decay' of stellar activity at the low-mass end of the main sequence is related to observational data. The data from Einstein and EXOSAT missions that correspond to these issues are found to be sparse, and more observational work is found to be necessary. Also, it is concluded that some issues need to be addressed, such as the X-ray dividing line in evolved stars and the absence of X-ray emission from dA stars. The related observational requirements and instrumental capabilities are given for each significant research focus.

Rosner, Robert↗
NASA NTRS1990

Future X-ray observations of 'normal' galaxies

The study of the X-ray properties of galaxies is discussed in terms of existing observational results and the capacity for interpreting the data. The NASA Einstein Observatory data is first examined to describe the X-ray properties of spiral and irregular galaxies as well as elliptical and SO galaxies. Issues that remain to be addressed can be explored by studying the X-ray properties of very luminous 'super-Eddington' sources, starburst galaxies, and different phases of the interstellar medium. The specific requirements are set forth for the observatories conducting the research; particular conditions are given for detecting galaxies, high-resolution studies of individual galaxies, bandwidth, spectral studies, and time-variability studies. An ideal X-ray telescope is described based on these conditions, the primary features of which are a collecting area greater than 100 sq m, a large bandwidth, and the capacity for both photometric and spectroscopic investigation.

Fabbiano, Giuseppina↗
NASA NTRS1990

Optical techniques for determination of normal shock position in supersonic flows for aerospace applications

Techniques for the quantitative determination of shock position in supersonic flows using direct and indirect methods is presented. A description of an experimental setup is also presented, different configurations of shock position sensing systems are explained, and some experimental results are given. All of the methods discussed are analyzed to determine the ease of technology transfer from the laboratory to in-flight operation.

Adamovsky, Grigory↗
NASA NTRS1990

A Detailed Investigation of Staged Normal Injection into a Mach 2 Flow

A study of the staged injection of two jets of air behind a rearward facing step into a Mach 2 flow was performed using the SPARK 3-D Navier-Stokes code. Calculated mole fraction distributions were compared with an extensive set of planar mole fraction measurements made with a laser induced iodine fluorescence technique. A statistical measure, the standard deviation, was used to help assess agreement between calculation and experiment. Overall, good agreement was found between calculated and measured values. Generally, agreement was better in the far field of the injectors. The effect of grid resolution was investigated by calculating solutions on grids of 60,000, 200,000, and 450,000 points. Differences in the solutions on the two finer grids were small. However, the mole fraction distributions were distinguishable. The effect of turbulence modeling was investigated by employing three different algebraic models for the jet turbulence: the Baldwin-Lomax model, the Prandtl mixing length model, and the Eggers mixing length model. Overall, the Eggers mixing length model was found to be superior for this case. Finally, the effect of the jet exit conditions was examined. A recently proposed Mach number distribution at the jet exit was found to slightly improve agreement between measurement and calculation.

Eklund, Dean R.↗
NASA NTRS1990

Digital carrier demodulator employing components working beyond normal limits

In a digital device, having an input comprised of a digital sample stream at a frequency F, a method is disclosed for employing a component designed to work at a frequency less than F. The method, in general, is comprised of the following steps: dividing the digital sample stream into odd and even digital samples streams each at a frequency of F/2; passing one of the digital sample streams through the component designed to work at a frequency less than F where the component responds only to the odd or even digital samples in one of the digital sample streams; delaying the other digital sample streams for the time it takes the digital sample stream to pass through the component; and adding the one digital sample stream after passing through the component with the other delayed digital sample streams. In the specific example, the component is a finite impulse response filter of the order ((N + 1)/2) and the delaying step comprised passing the other digital sample streams through a shift register for a time (in sampling periods) of ((N + 1)/2) + r, where r is a pipline delay through the finite impulse response filter.

Hurd, William J.↗
NASA NTRS1992

Influence of mass moment of inertia on normal modes of preloaded solar array mast

Earth-orbiting spacecraft often contain solar arrays or antennas supported by a preloaded mast. Because of weight and cost considerations, the structures supporting the spacecraft appendages are extremely light and flexible; therefore, it is vital to investigate the influence of all physical and structural parameters that may influence the dynamic behavior of the overall structure. The study primarily focuses on the mast for the space station solar arrays, but the formulations and the techniques developed in this study apply to any large and flexible mast in zero gravity. Furthermore, to determine the influence on the circular frequencies, the mass moment of inertia of the mast was incorporated into the governing equation of motion for bending. A finite element technique (MSC/NASTRAN) was used to verify the formulation. Results indicate that when the mast is relatively flexible and long, the mass moment inertia influences the circular frequencies.

Armand, Sasan C.↗