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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Seasonal nitrous oxide flux from an intensively managed pasture in a humid subtropical ecosystem

Nitrous oxide (N2O) flux from vented chambers was measured over intensively and minimally managed bermuda grass hay meadows in a humid, subtropical ecosystem for several years during scheduled sampling protocol following harvest, fertilization and rainfall events while measuring diel N2O emissions once during each of 5 seasonal day growth cycles which divided each calendar year. Soil pools of nitrite NO2(-), nitrate NO3(-), and ammonia (NH3) were measured in soil samples taken at 2 and 10 cm depths during each emission collection to determine transformations of the nitrogen pools coupled with N2O emissions. The highest diel N2O emission occur midday in the Spring cycle, measuring 9.0 g N/ha/d only for several weeks, while emissions dropped to less than 1.0 g N/ha/day during hot, dry, and colder months. Intensively managed meadows (4 fertilizations and harvests per year plus pest management) induced higher seasonal N2O emissions than minimal treatment (1 fertilization and harvest) averaging 2.75 and 5.97 g N/ha/day. Nitrous oxide emission data as responses to soil parameters and environmental parameters were also measured where air temperature, soil moisture, and fertilization were the most powerful factors.

Brams, Eugene A.↗
NASA NTRS1991

A relative-intensity two-color phosphor thermography system

The NASA LaRC has developed a relative-intensity two-color phosphor thermography system. This system has become a standard technique for acquiring aerothermodynamic data in LaRC Hypersonic Facilities Complex (HFC). The relative intensity theory and its application to the LaRC phosphor thermography system is discussed along with the investment casting technique which is critical to the utilization of the phosphor method for aerothermodynamic studies. Various approaches to obtaining quantitative heat transfer data using thermographic phosphors are addressed and comparisons between thin-film data and thermographic phosphor data on an orbiter-like configuration are presented. In general, data from these two techniques are in good agreement. A discussion is given on the application of phosphors to integration heat transfer data reduction techniques (the thin film method) and preliminary heat transfer data obtained on a calibration sphere using thin-film equations are presented. Finally, plans for a new phosphor system which uses target recognition software are discussed.

Merski, N. Ronald↗
NASA NTRS1990

Three-dimensional stress intensity factor analysis of a surface crack in a high-speed bearing

The boundary element method is applied to calculate the stress intensity factors of a surface crack in the rotating inner raceway of a high-speed roller bearing. The three-dimensional model consists of an axially stressed surface cracked plate subjected to a moving Hertzian contact loading. A multidomain formulation and singular crack-tip elements were employed to calculate the stress intensity factors accurately and efficiently for a wide range of configuration parameters. The results can provide the basis for crack growth calculations and fatigue life predictions of high-performance rolling element bearings that are used in aircraft engines.

Ballarini, Roberto↗
NASA NTRS1991

The physical properties of giant molecular cloud complexes in the outer Galaxy - Implications for the ratio of H2 column density to (C-12)O intensity

The physical properties of 35 giant molecular cloud complexes in the outer Galaxy were derived from the Goddard-Columbia surveys of the Galactic plane region (Dame et al., 1987). The spatial and radial velocity boundaries for the individual cloud complexes were estimated by analyzing the spatial and velocity structure of emission features in the (C-12)O surveys, and the distance to each cmplex was determined kinematically on the assumption of a flat rotation curve. The ratio of the H2 column density to the (C-12)O intensity for the outer Galaxy complexes was found to be about 6.0 x 10 to the 20th molecules/sq cm K per km/sec, which is by a factor of 2-3 greater than the value derived by other auhtors for the inner Galaxy complexes. This increase in the H2 column density/(C-12)O intensity with the distance from with the Galactic center is consistent with predictions of the optically thick cloudlet model of giant molecular cloud complexes.

Sodroski, T. J.↗
NASA NTRS1991

Stress intensity factors for large aspect ratio surface and corner cracks at a semi-circular notch in a tension specimen

Stress intensity factor solutions for semielliptic surface and quarter-elliptic corner cracks emanating from a semicircular notch in a tension specimen are presented. A three-dimensional finite-element analysis in conjunction with the equivalent domain integral was used to calculate stress intensity factors (SIF). SIF solutions for surface or corner crack (crack length to depth ratio of 2) at a notch are presented for a wide range of crack sizes and notch radii. Results showed that the SIF are larger for larger crack lengths and for larger notch radii. The SIF are nearly constant all along the crack front for deep surface cracks and for all corner cracks analysed.

Shivakumar, K. N.↗
NASA NTRS1991

Measurements of Lorentz air-broadening coefficients and relative intensities in the H2O-16 pure rotational and nu2 bands from long horizontal path atmospheric spectra

Lorentz air-broadening coefficients and relative intensities have been measured for forty-three lines in the pure rotational band and twenty lines in the nu2 band of H2O-16 between 800 and 1150/cm. The results were derived from analysis of nine 0.017/cm-resolution atmospheric absorption spectra recorded over horizontal paths of 0.5-1.5 km with the McMath Fourier transform spectrometer and main solar telescope operated on Kitt Peak by the National Solar Observatory. A nonlinear least-squares spectral fitting technique was used in the spectral analysis. The results are compared with previous measurements and calculations. In most cases, the measured pressure-broadening coefficients and intensities are significantly different from the values in the 1986 HITRAN line parameters compilation.

Rinsland, Curtis P.↗
NASA NTRS1991

A simple method for correcting spatially resolved solar intensity oscillation observations for variations in scattered light

A measurement of the intensity distribution in an image of the solar disk will be corrupted by a spatial redistribution of the light that is caused by the earth's atmosphere and the observing instrument. A simple correction method is introduced here that is applicable for solar p-mode intensity observations obtained over a period of time in which there is a significant change in the scattering component of the point spread function. The method circumvents the problems incurred with an accurate determination of the spatial point spread function and its subsequent deconvolution from the observations. The method only corrects the spherical harmonic coefficients that represent the spatial frequencies present in the image and does not correct the image itself.

Jefferies, S. M.↗
NASA NTRS1991

Forbidden lines of np(q) ions. II - Line intensities

Ground state forbidden transitions of np(q) ions of C, N, O, Ne, Mg, Si, S, and Fe can provide important information on the state of cosmic ionized gases. The line intensities of 95 transitions of these ions have been tabulated, including those used to calculate the line ratios as well as other strong lines of the ions in the ground state terms in the same temperature and density ranges treated previously. These data can be used for calculations of the absolute line intensities if the ionic abundances are known. These calculations are important for studies of the solar transition region, ionized nebulae, circumstellar nebulae such as found in symbiotic stars, supernova remnants, interstellar bubbles produced by stellar winds, and emission regions in active galactic nuclei.

Lynch, John P.↗
NASA NTRS1991

Intensity variation and coherence of 3-6 day equatorial waves

Meridional wind oscillations of 3-6 day period are common in the equatorial lower stratosphere. Upper air data obtained from 32 equatorial stations, 1973-87, show that 70 mb wave intensity over the Maritime continent varied annually with largest amplitude in NH late winter and spring, but the seasonal cycle of intensity was not uniform in the tropics. Time series of meridional velocity and its spatial coherence suggest that 70 mb wave packets were local in longitude and episodic in time.

Dunkerton, Timothy J.↗
NASA NTRS1992

Sound power determination using the sound intensity scanning technique

A technique is presented for determining sound power from sound intensity measurements. Sound power from sound pressure measurements needs approximations, a specific measurement environment, and costly facilities. Sound intensity measurements are the primary quantity required to determine sound power levels, require no costly facilities, and can be made in the presence of extraneous noise. All results are presented in viewgraph format.

Krishnappa, G.↗
NASA NTRS1991

Probe systems for static pressure and cross-stream turbulence intensity

A recent study of total-pressure probes for use in highly turbulent streams is extended herein by developing probe systems that measure time-averaged static or ambient pressure and turbulence intensity. Arrangements of tubular probes of circular and elliptical cross section are described that measure the pressure at orifices on the sides of the probes to obtain different responses to the cross-stream velocity fluctuations. When the measured data are combined to remove the effect of the presence of the probes on the local pressure, the time-averaged static pressure and the cross-stream components of turbulence intensity can be determined. If a system of total pressure tubes, as described in an accompanying paper, is added to the static pressure group to form a single cluster, redundant measurements are obtained that permit accuracy and consistency checks.

Rossow, Vernon, J.↗
NASA NTRS1990

Three-dimensional simulation of the Denver 11 July Storm of 1988 - An intense microburst event

An account is given of results from a numerical simulation of an intense microburst-generating storm observed near Denver during a test operation of the Terminal Doppler Radar System, on July 11, 1988. The numerical simulation encompassed comparisons with 'observed' data from measurements by Doppler radar, aircraft flight data recorders, and surface field instruments. Model results are in excellent qualitative and quantitative agreement with major storm feature observations. The intense microburst that was generated some distance 'downshear' of the primary precipitation area was driven by cooling due to sublimating snow.

Proctor, Fred H.↗
NASA NTRS1992

Intensity and linewidth measurements in the 13.7-micron fundamental bands of (C-12)2H2 and (C-12)(C-13)H2 at planetary atmospheric temperatures

The absolute intensities and collision-broadened half-widths of several lines in the P-,Q-, and R-branches of the nu5-fundamental band of (C-12)2H2 have been measured at various temperatures between 147 and 295 K employing the Doppler-limited spectral resolution (about 10 exp -4/cm) of a tunable diode laser spectrometer. The absolute intensities of R(5), R(7), R(9), and R(20) in the same fundamental belonging to (C-12)(C-13)H2 have also been measured at 294 K. The temperature dependence of the collision-broadened half-width has been determined for some of the lines broadened by planetary atmospheric gases, namely, He, Ar, H2, and N2. Four self-broadened linewidths of (C-12)2H2, as well as three H2-broadened linewidths and a self-broadened half-width of (C-12)(C-13)H2, have also been retrieved from the measurements.

Varanasi, Prasad↗
NASA NTRS1992

Propagation of a large Forbush decrease in cosmic-ray intensity past the earth, Pioneer 11 at 34 AU and Pioneer 10 at 53 AU

Observations of a large Forbush decrease in cosmic-ray intensity at the earth, Pioneer II and Pioneer 10 are reported. The Pioneer 10 data show a large impulsive decrease in cosmic-ray intensity at the greatest distance from the sun observed to date. The apparent radial speed of propagation of the Forbush decrease was about 820 km/s, independent of the radial distance. The observations reported here and similar previous observations provide the basis for a new quantitative model of the propagation of Forbush decreases in the outer heliosphere.

Van Allen, James A.↗
NASA NTRS1992

A numerical field experiment approach for determining probabilities of microburst intensity

Several investigators had determined that some atmospheric parameters were related to the formation and severity of microbursts. For example, Caracena pointed out the relationship between a dry adiabatic lapse rate and microbursts in 'The crash of Delta Flight 191 at Dallas-Fort Worth international airport'. These early investigations led to the idea that numeric modeling of microbursts with varying atmospheric parameters might define 'signatures' that could lead to determining the probability of microburst intensity. The idea was that, by using already available sensors (such as static air temperature, pressure altitude, and radar reflectivity) onboard an aircraft, a reliable prediction of microburst existence and intensity could be formed. Such data could be used to create an 'expert meteorologist' using either artificial intelligence or other techniques that could be used in either reactive or look-ahead systems to vary sensitivity thresholds and coordinate the inputs from different detecting systems. To this end, Honeywell contracted to have the microburst simulations run. The questions to be addressed were the following: using the sensor set available to the aircraft (e.g. temperature, radar reflectivity, etc.), can we calculate the probability that (1) a microburst could be formed? and (2) that the resultant winds would be of sufficient magnitude to threaten the aircraft? Over a two year period, a data set of 1800 microburst simulations was accumulated. Verification of the microburst simulation was obtained using the results of other independent researchers and actual comparison to microburst events in Orlando and Denver. Some of the results from the simulation have already been incorporated into Honeywell's Windshear Detection and Guidance System with excellent results. Various aspects of this investigation are presented in viewgraph form.

Droegemeier, Kelvin K.↗
NASA NTRS1992

Line intensities and collisional-broadening parameters for the nu4 and nu6 bands of carbonyl fluoride

Line intensities, air- and self-broadening parameters have been measured for selected lines in the nu4 (1243/cm) and nu6 (774/cm) bands of carbonyl fluoride at 296 and 215 K using a tunable diode-laser spectrometer. Measured line intensities are in good agreement +/- 6 percent with recently reported values derived from rotational analyses of the nu4 and nu6 bands. The measured average air-broadening coefficient at 296 K also agrees well (+/- 5 percent) with N2-broadening coefficients determined from microwave studies, while the average self-broadening coefficient reported here is smaller than a previously reported value by 45 percent.

May, Randy D.↗
NASA NTRS1993

Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster /(t-Bu)GaS/4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

Macinnes, Andrew N.↗