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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 1,513 records · Page 84
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NASA NTRS1988

Transverse ion energization and low-frequency plasma waves in the mid-altitude auroral zone - A case study

Evidence of transverse ion energization at altitudes of several earth radii in the auroral zone was reexamined using several hundred hours of high-sensitivity and high-resolution plasma data obtained by the Dynamics Explorer 1 satellite. The data on particle environment encountered at midaltitudes in the auroral zone disclosed rapid variations in the values of total density, thermal structure, and composition of the plasma in the interval measured; the modes of low-frequency plasma waves also varied rapidly. It was not possible to unambiguously identify in these data particle and wave signature of local transverse ion energization; however, many intervals were found where local transverse ion heating was consistent with the observations.

Peterson, W. K.↗
NASA NTRS1988

Extraction of topography from side-looking satellite systems - A case study with SPOT simulation data

A simulated data set was used to evaluate techniques for extracting topography from side-looking satellite systems for an area of northwest Washington state. A negative transparency orthophotoquad was digitized at a spacing of 85 microns, resulting in an equivalent ground distance of 9.86 m between pixels and a radiometric resolution of 256 levels. A bilinear interpolation was performed on digital elevation model data to generate elevation data at a 9.86-m resolution. The nominal orbital characteristics and geometry of the SPOT satellite were convoluted with the data to produce simulated panchromatic HRV digital stereo imagery for three different orbital paths and techniques for reconstructing topographic data were developed. Analyses with the simulated HRV data and other data sets show that the method is effective.

Ungar, Stephen G.↗
NASA NTRS1988

Use of four-dimensional data assimilation by Newtonian relaxation and latent-heat forcing to improve a mesoscale-model precipitation forecast - A case study

The Penn State/NCAR mesoscale model was used to study special static-initialization (SI) and dynamic-initialization (DI) techniques designed to improve short-range quantitative precipitation forecasts (QPFs), as applied to the heavy convective rainfall that occurred in Texas, Oklahoma, and Kansas during the May 9-10, 1979 SESAMY IV study period. In the DI procedure, two types of four-dimensional data assimilation (FDDA) procedures were used to incorporate data during a 12-h preforecast period, one using the Newtonian relaxation, the other using latent-heat forcing. It was found that combined use of either the preforecast or in-forecast latent-heat forcing with the Newtonian relaxation produced an improved forecast (relative to a conventional forecast procedure) of rainfall intensity compared to the use of the Newtonian relaxation alone. The use of the experimental SI with prescribed latent heating during the first forecast hour produced greatly improved rainfall rates.

Wang, Wei↗
NASA NTRS1989

A case study of a WC planetary nebula nucleus - Henize 2-99

The WC spectrum of the nucleus of the planetary nebula Henize 2-99. Fluxes are given, emission lines are identified, and blends are described. The most powerful emissions are C III, C II, and C IV. O, H, and Si lines are also observed, but little stellar nitrogen is found except for N V. The interstellar extinction is estimated at c = 0.9 + or - 0.2. Blackbody, Zanstra, and Stoy temperatures are found to be 70,000 K, 26,000 K, and 27,000 K, respectively. It is shown that He 2-99 is binebulous with a prominent enhancement in H-alpha along the minor axis. The structural characteristics of He 2-99 are very similar to BD +30 deg 3639 and NGC 40.

Kaler, James B.↗
NASA NTRS1989

A multiloop, digital flutter suppression control law synthesis case study

A methodology for obtaining a digital low-order, multiloop, robust control law for aeroelastic application from a full-state Linear Quadratic Gaussian design is presented. As part of the design methodology, the multivariable system robustness at the plant input and output is evaluated using singular value properties and improved using constrained optimization procedures. To validate the methodology, a digital flutter suppression system has been designed for the full-span Active Flexible Wing (AFW) wind-tunnel model as part of a collaborative effort between the NASA Langley Research Center and Rockwell International. Preliminary results for a low-order discrete, symmetric flutter suppression system design that significantly improved the AFW model stability are provided and the experiences gained during the design process are discussed.

Mukhopadhyay, Vivek↗
NASA NTRS1989

A case study of a low lightning rate storm during the Florida winter

Meteorological and cloud electrical data collected during a winter storm on January 21, 1988 at the Kennedy Space Center (KSC) in Florida are presented. A pronounced transition from area-integrated convergence to divergence with associated peak electrical activity was observed, which appears to be characteristic for both the summer and the winter storms at KSC. The mesoscale precipitation region behind the squall line was substantially electrified over an area far larger than the KSC complex. It is noted that, in such a situation, the accumulated electric charge and peak lightning currents may be an order of magnitude greater than those encountered in isolated summer thunderstorms, and the lightning hazard is correspondingly greater.

Williams, Earle R.↗
NASA NTRS1989

The Materials Division: A case study

The Materials Division at NASA's Lewis Research Center has been engaged in a program to improve the quality of its output. The division, its work, and its customers are described as well as the methodologies developed to assess and improve the quality of the Division's staff and output. Examples of these methodologies are presented and evaluated. An assessment of current progress is also presented along with a summary of future plans.

Grisaffe, Salvatore J.↗
NASA NTRS1989

Report of the NASA lunar energy enterprise case study task force

The Lunar Energy Enterprise Cast Study Task Force was formed to determine the economic viability and commercial business potential of mining and extracting He-3 from the lunar soil for use in earth-based fusion reactors. In addition, the Solar Power Satellite (SPS) and the Lunar Power Station (LPS) were also evaluated because they involve the use of lunar materials and could provide energy for lunar-based activities. The Task Force considered: (1) the legal and liability aspects of the space energy projects; (2) the long-range terrestrial energy needs and options; (3) the technical maturity of the three space energy projects; and (4) their commercial potential. The use of electricity is expected to increase, but emerging environmental concerns and resource availability suggest changes for the national energy policy. All three options have the potential to provide a nearly inexhaustible, clean source of electricity for the U.S. and worldwide, without major adverse impacts on the Earth's environment. Assumption by industry of the total responsibility for these energy projects is not yet possible. Pursuit of these energy concepts requires the combined efforts of government and industry. The report identifies key steps necessary for the development of these concepts and an evolving industrial role.

Source record↗
NASA NTRS1989

Transient fault behavior in a microprocessor: A case study

An experimental analysis is described which studies the susceptibility of a microprocessor based jet engine controller to upsets caused by current and voltage transients. A design automation environment which allows the run time injection of transients and the tracing from their impact device to the pin level is described. The resulting error data are categorized by the charge levels of the injected transients by location and by their potential to cause logic upsets, latched errors, and pin errors. The results show a 3 picoCouloumb threshold, below which the transients have little impact. An Arithmetic and Logic Unit transient is most likely to result in logic upsets and pin errors (i.e., impact the external environment). The transients in the countdown unit are potentially serious since they can result in latched errors, thus causing latent faults. Suggestions to protect the processor against these errors, by incorporating internal error detection and transient suppression techniques, are also made.

Duba, Patrick↗
NASA NTRS1989

The 27-28 October 1986 FIRE IFO Cirrus case study: Comparison of radiative transfer theory with observations by satellite and aircraft

Observations of cirrus and altocumulus clouds during the First International Satellite Cloud Climatology Project Regional Experiment (FIRE) are compared to theoretical models of cloud radiative properties. Three tests are performed. First, LANDSAT radiances are used to compare the relationship between nadir reflectance ot 0.83 micron and beam emittance at 11.5 microns with that predicted for model calculations using spherical and nonspherical phase functions. Good agreement is found between observations and theory when water droplets dominate. Poor agreement is found when ice particles dominate, especially using scattering phase functions for spherical particles. Even when compared to a laboratory measured ice particle phase function, the observations show increased side scattered radiation relative to the theoretical calculations. Second, the anisotropy of conservatively scattered radiation is examined using simultaneous multiple angle views of the cirrus from LANDSAT and ER-2 aircraft radiometers. Observed anisotropy gives good agreement with theoretical calculations using the laboratory measured ice particle phase function and poor agreement with a spherical particle phase function. Third, Landsat radiances at 0.83, 1.65, and 2.21 microns are used to infer particle phase and particle size. For water droplets, good agreement is found with King Air FSSP particle probe measurements in the cloud. For ice particles, the LANDSAT radiance observations predict an effective radius of 60 microns versus aircraft observations of about 200 microns. It is suggested that this descrepancy may be explained by uncertainty in the imaginary index of ice and by inadequate measurements of small ice particles by microphysical probes.

Wielicki, Bruce A.↗
NASA NTRS1989

The 27-28 October 1986 FIRE IFO cirrus case study: Cirrus parameter relationships derived from satellite and lidar data

Cirrus cloud radiative and physical characteristics are determined using a combination of ground-based, aircraft, and satellite measurements taken as part of the First ISCCP Regional Experiment (FIRE) Cirrus Intensive Field Observations (IFO) during October and November 1986. Lidar backscatter data are used to define cloud base, center, and top heights and the corresponding temperatures. Coincident GOES 4 km visible (0.65 microns) and 8 km infrared window (11.5 microns) radiances are analyzed to determine cloud emittances and reflectances. Infrared optical depth is computed from the emittance results. Visible optical depth is derived from reflectance using a theoretical ice crystal scattering model and an empirical bidirectional reflectance mode. No clouds with visible optical depths greater than 5 or infrared optical depths less than 0.1 were used in the analysis. Average cloud thickness ranged from 0.5 km to 8 km for the 71 scenes. An average visible scattering efficiency of 2.1 was found for this data set. The results reveal a significant dependence of scattering efficiency on cloud temperature.

Minnis, Patrick↗
NASA NTRS1990

A stratocumulus thermodynamic analysis: July 5 case study

On July 5 (NCAR Electra flight 4, Mission 186-G) the Electra flew a single aircraft mission which consisted of cross and along-wind legs at 6 different altitudes between 10:43 to 16:00 PDT (17:43 to 23:00 GMT). The leg length was kept short (8 to 10 minutes) to permit maximum vertical resolution, and there were 8 soundings. Observer notes report a thin, solid stratocumulus cloud deck which gradually became more broken in the afternoon. Winds were from the north at 10 to 13/ms throughout the night. Sea surface temperature measurements and conservative variable analyses for several of the July 5 legs are presented. These results are preliminary to a study of the thermodynamic budget on July 5; they indicate that: the sea surface temperature dropped more than 1 K (from 17.3 to 15.9 C) over the course of the flight (18:01 and at 21:51 GMT); mixing lines for each of the horizontal subcloud legs show the effect of a strong north-south gradient in SST; and there is a clear demarcation over a transition of 5 to 10 km between air to the south and cooler, moister air to the north. The FSSP measurements indicate there are small clouds/scud 250 m below cloud base on the cold northern side of this transition. The transition is seen in the saturation point diagrams at 984, 959, and 946 mb. There is no corresponding change in the horizontal wind across the transition regions.

Austin, Philip↗
NASA NTRS1990

A case study of cumulus formation beneath a stratocumulus sheet: Its structure and effect on boundary layer budgets

On several occasions during the FIRE Marine Stratocumulus IFO off the California coast, small cumulus were observed to form during the morning beneath the main stratocumulus (Sc) deck. This occurs in the type of situation described by Turton and Nicholls (1987) in which there is insufficient generation of turbulent kinetic energy (TKE) from the cloudtop or the surface to sustain mixing throughout the layer, and a separation of the surface and cloud layers occurs. The build up of humidity in the surface layer allows cumuli to form, and the more energetic of these may penetrate back into the Sc deck, reconnecting the layers. The results presented were collected by the UKMO C-130 aircraft flying in a region where these small cumulus had grown to the extent that they had penetrated into the main Sc deck above. The structure of these penetrative cumulus are examined and their implications on the layer flux and radiation budget discussed.

Barlow, Roy W.↗
NASA NTRS1990

The October 27-28, 1986, FIRE cirrus case study: Cloud microstructure

Using aircraft in-situ measurements, the microphysics of cirrus clouds observed on 28 Oct. 1986 during FIRE were examined. Results are presented as one component of a coordinated study of the cirrus on the day. The study contributes to the understanding of cold clouds by: (1) providing microphysical data to supplement satellite and aircraft data for investigating cirrus cloud radiative effects; (2) providing more complete information on ice particle evolution and cloud forcing mechanisms than has been available through the use of instrumentation with higher resolution and more accurate calibration; (3) expanding the knowledge of the particle characteristics in cold liquid water clouds, through improved instrumentation and by making use of sensors on other platforms, such as lidar; and (4) by estimating the ice nucleus concentrations active at low temperatures in the upper troposphere from the concentrations of ice particles in colloidally stable liquid water clouds.

Miller, Karen M.↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study: Comparison of satellite and aircraft derived particle size

Theoretical calculations predict that cloud reflectance in near infrared windows such as those at 1.6 and 2.2 microns should give lower reflectances than at visible wavelengths. The reason for this difference is that ice and liquid water show significant absorption at those wavelengths, in contrast to the nearly conservative scattering at wavelengths shorter than 1 micron. In addition, because the amount of absorption scales with the path length of radiation through the particle, increasing cloud particle size should lead to decreasing reflectances at 1.6 and 2.2 microns. Measurements at these wavelengths to date, however, have often given unpredicted results. Twomey and Cocks found unexpectedly high absorption (factors of 3 to 5) in optically thick liquid water clouds. Curran and Wu found expectedly low absorption in optically thick high clouds, and postulated the existence of supercooled small water droplets in place of the expected large ice particles. The implications of the FIRE data for optically thin cirrus are examined.

Wielicki, Bruce A.↗
NASA NTRS1989

Reasoning about software specifications - A case study

The launch intercept condition (LIC) problem was analyzed to better understand the complexity of the automated reasoning process and the nature and role of background knowledge. An extension to resolution-based logic processing systems, called constraint logic programming, is described. Consideration is also given to a knowledge-driven incremental reasoning architecture which integrates a generic constraint logic programming system with a knowledge base of the domain.

Wild, Chris↗
NASA NTRS1989

A case study using kinematic quantities derived from a triangle of VHF Doppler wind profilers

Horizontal divergence, relative vorticity, kinematic vertical velocity, and geostrophic and ageostrophic winds are computed from Colorado profiler network data to investigate an upslope snowstorm in northeastern Colorado. Horizontal divergence and relative vorticity are computed using the Gauss and Stokes theorems, respectively. Kinematic vertical velocities are obtained from the surface to 9 km by vertically integrating the continuity equation. The geostrophic and ageostrophic winds are computed by applying a finite differencing technique to evaluate the derivatives in the horizontal equations of motion. Comparison of the synoptic-scale data with the profiler network data reveals that the two datasets are generally consistent. Also, the profiler-derived quantities exhibit coherent vertical and temporal patterns consistent with conceptual and theoretical flow fields of various meteorological phenomena. It is suggested that the profiler-derived quantities are of potential use to weather forecasters in that they enable the dynamic and kinematic interpretation of weather system structure to be made and thus have nowcasting and short-term forecasting value.

Carlson, Catherine A.↗
NASA NTRS1989

A case study of wave-current interaction near an oceanic front

High resolution directional wave spectrum data were obtained from two NASA airborne radars during the Frontal Air-Sea Interaction Experiment in February 1986. The observations show a significant change in the wave number spectrum across the front. On the basis of surveys from a towed sensor and on satellite imagery, the front location and current field are estimated. A numerical model is developed for the wave-current interaction and is used to model the wave refraction across the frontal current. A parametric study is performed to demonstrate the effects of current meandering. The main consequence of meandering is the formation of caustics and shadow zone regions in which the wave energy is significantly enhanced or reduced. Spectral simulation along the aircraft track reveals a reduction of more that 60 percent in wave energy in the shadow zone; this is consistent with the observations.

Liu, A. K.↗