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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 451 records · Page 25
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NASA NTRS1976

Results from the Ariel 5 All-Sky Monitor

Results are summarized for the first year of operation of the Ariel 5 All-Sky Monitor. The monitor is described in detail, and representative observations of the transient sources A1524-62, Cen X-mas, A0535+26, and A0620-00 are discussed. It is shown that the transients are largely confined to the galactic plane and that about 100 such sources per year can be expected in the Galaxy. Long-term observations of Sco X-1, Cyg X-3, and Cyg X-1 are reported which illustrate that the large intensity variations in Sco X-1 appear to correlate on time scales greater than one Ariel 5 orbit, that Cyg X-3 has a widely varying intensity, and that the predominant feature of the intensity variation in Cyg X-1 is a minimum near superior conjunction.

Holt, S. S.↗
NASA NTRS1977

Three-dimensional vector modeling and restoration of flat finite wave tank radiometric measurements

In this paper, a three-dimensional Fourier transform inversion method describing the interaction between water surface emitted radiation from a flat finite wave tank and antenna radiation characteristics is reported. The transform technique represents the scanning of the antenna mathematically as a correlation. Computation time is reduced by using the efficient and economical fast Fourier transform algorithm. To verify the inversion method, computations have been made and compared with known data and other available results. The technique has been used to restore data of the finite wave tank system and other available antenna temperature measurements made at the Cape Cod Canal. The restored brightness temperatures serve as better representations of the emitted radiation than the measured antenna temperatures.

Truman, W. M.↗
NASA NTRS1978

Some two-point statistical properties of a three-dimensional wall jet

The effects of both a straight and a curved wall on the two-point space-time velocity correlations of a turbulent jet are documented. From the correlations, isocorrelation contours are constructed which allow a picture of the various flow patterns to be determined. Autoand cross-correlations of the fluctuating concentration field are also obtained for the different flow configurations. The confining surfaces served to radically change the flow pattern for the freely expanding turbulent jet. The velocity measurements are made with a laser Doppler velocimeter in conjunction with a phase locked-loop processor, while the concentration field is monitored with a laser light-scattering technique.

Morton, J. B.↗
NASA NTRS1979

Contribution to the study of turbulence spectra

An apparatus suitable for turbulence measurement between ranges of 1 to 5000 cps and from 6 to 16,000 cps was developed and is described. Turbulence spectra downstream of the grills were examined with reference to their general characteristics, their LF qualities, and the effects of periodic turbulence. Medium and HF are discussed. Turbulence spectra in the boundary layers are similarly examined, with reference to their fluctuations at right angles to the wall, and to lateral fluctuations. Turbulence spectra in a boundary layer with suction to the wall is discussed. Induced turbulence, and turbulence spectra at high Reynolds numbers. Calculations are presented relating to the effect of filtering on the value of the correlations in time and space.

Dumas, R.↗
NASA NTRS1978

The dependence of solar flare energetics on flare volumes

The sizes of 45 X-ray flares observed on Skylab have been measured and compared to flare rise times, energies, and energy release rates as determined from Solard and XREA X-ray data. The X-ray rise time is correlated with the length and volume of the flare. The energy of the flare and the rate of increase of that energy are correlated with flare length and volume. Both the energy per unit volume and the rate of energy increase per unit volume are inversely correlated with flare length and volume. There is no correlation between the emission measure and the volume.

Kahler, S. W.↗
NASA NTRS1979

Conditional replenishment using motion prediction

Conditional replenishment is an interframe video compression method that uses correlation in time to reduce video transmission rates. This method works by detecting and sending only the changing portions of the image and by having the receiver use the video data from the previous frame for the non-changing portion. The amount of compression that can be achieved through this technique depends to a large extent on the rate of change within the image, and can vary from 10 to 1 to less than 2 to 1. An additional 3 to 1 reduction in rate is obtained by the intraframe coding of data blocks using a 2-dimensional variable rate Hadamard transform coder. A further additional 2 to 1 rate reduction is achieved by using motion prediction. Motion prediction works by measuring the relative displacements of a subpicture from one frame to the next. The subpicture can then be transmitted by sending only the value of the 2-dimensional displacement. Computer simulations have demonstrated that data rates of 2 to 4 Mega-bits/second can be achieved while still retaining good fidelity in the image.

Hein, D. N.↗
NASA NTRS1979

Turbulence measurements in a three dimensional wall jet

The effects of both a straight and a curved wall on the two-point space-time velocity correlations of a turbulent jet are documented. From the correlations, iso-correlation contours are constructed which allow a picture of the various flow patterns to be determined. Auto and cross-correlations of the fluctuating concentration field are also obtained for the different flow configurations. The confining surfaces served to radically change the flow pattern of the freely expanding turbulent jet. The velocity measurements are made with a laser Doppler velocimeter in conjunction with a phase locked-loop processor, while the concentration field is monitored with a laser light scattering technique.

Catalano, G. D.↗
NASA NTRS1981

Evidence for the tailward retreat of a magnetic neutral line in the magnetotail during substorm recovery

Plasma sheet observations made during a substorm recovery at 0400 to 0430 UT on March 1, 1978 with the ISEE satellites strongly suggest that the observed field-aligned flow of plasma in the earthward direction has mirrored in the vicinity of the earth and returned to the position of the satellites to produce the tailward flow seen at this time. The correlation between the estimated speeds of the earthward and tailward moving distribution indicates that the observed changes in velocity are spatial rather than temporal. It is concluded that the movement of the plasma sheet surface results from the propagation of an energetic particle source on to new magnetic field lines which progressively map deeper into the tail and also to higher polar latitudes at the earth. The movement of the source onto new magnetic field lines is clearly consistent with the tailward retreat of a magnetic neutral line in the plasma sheet during substorm recovery.

Forbes, T. G.↗
NASA NTRS1981

Spatial and temporal structures of impulsive bursts from solar flares observed in UV and hard X-rays

New observations are presented of impulsive UV and hard X-rays bursts in two solar flares obtained with instruments on Solar Maximum Mission. The UV bursts were observed in the Si IV and O IV emission lines, whose intensity ratio is density-sensitive. By comparing the spatially resolved Si IV/O IV observations with the corresponding hard X-ray observations, it is possible to study their spatial and temporal relationships. For one flare, the individual component spikes in the multiply peaked hard X-ray burst can be identified with different discrete Si IV/O IV flaring kernels of size 4 arcsec x 4 arcsec or smaller, which brighten up sequentially in time. For the other, many Si IV/O kernels, widely distributed over a large area, show impulsive bursts at the same time, which correlate with the main peak of the impulsive hard X-ray burst. The density of the flaring Si IV/O IV kernels is in the range from 5 x 10 to the 12th-13th/cu cm.

Cheng, C.-C.↗
NASA NTRS1982

Measuring Hydrogen Properties in Aluminum

System in use at Langley Research Center measures concentration and diffusion coefficient of hydrogen in pure aluminum. Principal components are high-temperature ultra-high-vacuum furnace and quadrupole mass spectrometer. Quantities of hydrogen and other gases that evolve from heated metal are measured in real time and correlated with data on aluminum porosity.

Outlaw, R. A.↗
NASA NTRS1982

Effects of higher order control systems on aircraft approach and landing longitudinal handling qualities

An investigation of approach and landing longitudinal flying qualities, based on data generated using a variable stability NT-33 aircraft combined with significant control system dynamics is described. An optimum pilot lead time for pitch tracking, flight path angle tracking, and combined pitch and flight path angle tracking tasks is determined from a closed loop simulation using integral squared error (ISE) as a performance measure. Pilot gain and lead time were varied in the closed loop simulation of the pilot and aircraft to obtain the best performance for different control system configurations. The results lead to the selection of an optimum lead time using ISE as a performance criterion. Using this value of optimum lead time, a correlation is then found between pilot rating and performance with changes in the control system and in the aircraft dynamics. It is also shown that pilot rating is closely related to pilot workload which, in turn, is related to the amount of lead which the pilot must generate to obtain satisfactory response. The results also indicate that the pilot may use pitch angle tracking for the approach task and then add flight path angle tracking for the flare and touchdown.

Pasha, M. A.↗
NASA NTRS1985

The downshift of electron plasma oscillations in the electron foreshock region

Electron plasma oscillations in the earth's electron foreshock region are observed to shift above and below the local electron plasma frequency. As plasma oscillations shift downward from the plasma frequency, their bandwidth increases and their wavelength decreases. Observations of plasma oscillations well below the plasma frequency are correlated with times when ISEE 1 is far downstream of the electron foreshock boundary. Although wavelengths of plasma oscillations below the plasma frequency satisfy k x lambda-De approximately 1 the Doppler shift due to the motion of the solar wind is not sufficient to produce the observed frequency shifts. A beam-plasma interaction with beam velocities on the order of the electron thermal velocity is suggested as an explanation for plasma oscillations above and below the plasma frequency. Frequency, bandwidth, and wavelength changes predicted from the beam-plasma interaction are in good agreement with the observed characteristics of plasma oscillations in the foreshock region.

Fuselier, S. A.↗
NASA NTRS1986

Characterization of the relationship of the cure cycle chemistry to cure cycle processing properties

Dynamic Dielectric measurements made over a wide range of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics. The measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, it is probably the only convenient experimental technique for studying the polymerization process of going from a monomeric liquid of varying viscosity to a crosslinked, insoluble, high temperature solid. The objective of the research is to develop on-line dielectric instrumentation for quantitative nondestructive material evaluation and closed loop smart cure cycle control. The key is to relate the chemistry of the cure cycle process to the dielectric properties of the polymer system by correlating the time, temperature, and frequency dependent dielectric measurements with chemical characterization measurements. Measurement of the wide variation in magnitude of the complex permittivity with both frequency and state of cure, coupled with chemical characterization work, have been shown in the laboratory to have the potential to determine: resin quality, composition and age; cure cycle window boundaries; onset of flow and point of maximum flow; extent of and completion of reaction; evolution of volatiles; T sub g; and, crosslinking and molecular weight buildup.

Kranbuehl, D. E.↗
NASA NTRS1987

Overview of crew member energy expenditure during Shuttle Flight 61-8 EASE/ACCESS task performance

The energy expenditure of the Shuttle Flight 61-B crewmembers during the extravehicular performance of Experimental Assembly of Structures in EVA (EASE) and Assembly Concept of Construction of Space Structures (ACCESS) construction system tasks are reported. These data consist of metabolic rate time profiles correlated with specific EASE and ACCESS tasks and crew comments. Average extravehicular activity metabolic rates are computed and compared with those reported from previous Apollo, Shylab, and Shuttle flights. These data reflect total energy expenditure and not that of individual muscle groups such as hand and forearm. When correlated with specific EVA tasks and subtasks, the metabolic profile data is expected to be useful in planning future EVA protocols. For example, after experiencing high work rates and apparent overheating during some Gemini EVAs, it was found useful to carefully monitor work rates in subsequent flights to assess the adequacy of cooling garments and as an aid to preplanning EVA procedures. This presentation is represented by graphs and charts.

Horrigan, D. J.↗
NASA NTRS1987

Turbofan engine core noise source diagnostics

The paper describes a turbofan-engine measurement program utilizing a variety of diagnostic techniques to identify a source of core-generated noise which contributes to the overall external engine noise characteristics. Included in the turbofan engine diagnostics are data examination, time domain correlation, and frequency domain analysis. It is found that the turbulent pressure fluctuations within the combustor are a source for core noise which propagates through the nozzle and radiates to the far-field.

Karchmer, Allen M.↗
NASA NTRS1987

An optical processor for object recognition and tracking

The design and development of a miniaturized optical processor that performs real time image correlation are described. The optical correlator utilizes the Vander Lugt matched spatial filter technique. The correlation output, a focused beam of light, is imaged onto a CMOS photodetector array. In addition to performing target recognition, the device also tracks the target. The hardware, composed of optical and electro-optical components, occupies only 590 cu cm of volume. A complete correlator system would also include an input imaging lens. This optical processing system is compact, rugged, requires only 3.5 watts of operating power, and weighs less than 3 kg. It represents a major achievement in miniaturizing optical processors. When considered as a special-purpose processing unit, it is an attractive alternative to conventional digital image recognition processing. It is conceivable that the combined technology of both optical and ditital processing could result in a very advanced robot vision system.

Sloan, J.↗
NASA NTRS1988

Mass determination of neutrinos

A time-energy correlation method has been developed to determine the signature of a nonzero neutrino mass in a small sample of neutrinos detected from a distant source. The method is applied to the Kamiokande II (Hirata et al., 1987) and IMB (Bionta et al., 1987) observations of neutrino bursts from SN 1987A. Using the Kamiokande II data, the neutrino rest mass is estimated at 2.8 + 2.0, - 1.4 eV and the initial neutrino pulse is found to be less than 0.3 sec full width, followed by an emission tail lasting at least 10 sec.

Chiu, Hong-Yee↗
NASA NTRS1989

NH3 column abundances over Lauder, New Zealand

Gaseous NH3 has been observed in the atmosphere over central New Zealand with infrared absorption spectra. The amount of NH3 shows marked variability, which is strongly correlated with time of day and season. The pattern is similar to data obtained in Denver, Colorado, but is much more variable than data from Hampton, Virginia. The rapid variability indicates a residence time of 8 hours in some cases.

Murcray, Frank J.↗