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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A methodology for long range prediction of air transportation

The paper describes the methodology for long-time projection of aircraft fuel requirements. A new concept of social and economic factors for future aviation industry which provides an estimate of predicted fuel usage is presented; it includes air traffic forecasts and lead times for producing new engines and aircraft types. An air transportation model is then developed in terms of an abstracted set of variables which represent the entire aircraft industry on a macroscale. This model was evaluated by testing the required output variables from a model based on historical data over the past decades.

Ayati, M. B.↗
NASA NTRS1980

Distribution of oxygen in silicon and its effects on electronic characteristics on a microscale

The microdistribution of oxygen in silicon was obtained by scanning IR absorption in as grown Czochralski crystals. The crystals were subsequently submitted to various heat treatments. The profiles of the generated thermal donors were determined by spreading resistance measurements. Contrary to the prevailing views, it was found that the concentration of the activated thermal donors is not strictly a function of the oxygen concentration, but depends strongly on an additional factor, which was shown to be associated with vacancy concentration. These conclusions could only be reached on the basis of microscale characterization. In fact, commonly employed macroscale analysis has led to erroneous conclusions.

Gatos, H. C.↗
NASA NTRS1980

Practical aspects of silicon float zone crystal growth

The float zone (FZ) growth method for silicon crystallization has advantages and disadvantages when compared to the other principal growth method, the Czochralski (CZ) technique. CZ growth is attractive for the following reasons: large diameters, high single crystal yields, low thermal gradients, low operator skill requirements, efficient power utilization, and low feed material costs. Some areas where FZ growth is advantageous include high purity, axial resistivity uniformity (on a macroscale), visibility of the growth region, low consumable material costs, and high growth rates.

Ciszek, T. T.↗
NASA NTRS1981

U.S. biological experiments in space

The history of biologic experimentation in space is traced. Early balloon and rocket borne animals showed no abnormalities on the macroscale, and biosatellite launches with bacteria and amoebae revealed no microscopic dysfunctions. Adult Drosophila flies on board Cosmos spacecraft died with a shortened lifespan, while their offspring lived full lifespans. Green pepper plants grown in weightlessness showed a different orientation, but no physiological disturbances. Normal bone growth in rats has been found to almost cease after 11 days in space, and the mean life span of red blood cells decreases by four days. A series of experiments designed by U.S. scientists will be performed on primates provided and flown by the U.S.S.R. Finally, experiments on board Spacelab will involve determination of the persistence of circadian rhythms in bacteria and humans.

Klein, H. P.↗
NASA NTRS1982

On the origin and spatial extent of high-latitude F region irregularities

Evidence for the direct production of macroscale irregularities by structured, soft electron fluxes is employed to form the basis for a model for the transport and decay of such structures and the role of plasma instabilities in the production of smaller irregularities. Large scale structures were defined with wavelengths of at least 10 km, intermediate between 0.0-10 km, and short less than 10 m. Data were gathered by means of a rocket flight into the auroral oval and radar scans of 10-350 km altitudes for electron density contours. The radar data indicated that the large-scale structure in the F region plasma was in the main due to electron precipitation. The instability of the structures caused the emergence of smaller scale irregularities in a dynamic balance of instability growth and damping. Additional productive sources which allow the greater than 100 km structures to pass over the North Pole intact are discussed.

Kelley, M. C.↗
NASA NTRS1985

Natural environment analysis

Qualitative analyses (and quantitatively to the extend possible) of the influence of terrain features on wind loading of the space shuttle while on the launch pad, or during early liftoff, are presented. Initially, the climatology and meteorology producing macroscale wind patterns and characteristics fot he Vandenburg Air Force Base (VAFB) launch site are described. Also, limited field test data are analyzed, and then the nature and characteristic of flow disturbances due to the various terrain features, both natural and man-made, are then reviewed. Following this, the magnitude of these wind loads are estimated. Finally, effects of turbulence are discussed. The study concludes that the influence of complex terrain can create significant wind loading on the vehicle. Because of the limited information, it is not possible to quantify the magnitude of these loads.

Source record↗
NASA NTRS1985

Natural environment analysis

The influence of terrain features on wind loading of the space shuttle while on the launch pad, or during early liftoff, was investigated both qualitatively and quantitatively. The climatology and meteorology producing macroscale wind patterns and characteristics for the Vandenburg Air Force Base launch site are described. Field test data are analyzed, and the nature and characteristic of flow disturbances due to the various terrain features, both natural and man-made, are reviewed. The magnitude of these wind loads are estimated. Finally, effects of turbulence are discussed. It is concluded that the influence of complex terrain can create significant wind loading on the vehicle.

Frost, W.↗
NASA NTRS1985

Coulomb collisions in the solar wind

A major improvement of the present investigation over previous studies of the subject is related to the use of helium temperatures obtained from helium ion measurements uncontaminated by the high-velocity tail of the proton distribution. More observations, covering a large parameter range, were employed, and the effects of interspecies drift were taken into account. It is shown in a more definite way than has been done previously, that Coulomb collisions provide the most important mechanism bringing about equilibrium between helium and protons in the solar wind. Other mechanisms may play some part in restricted regions, but Coulomb collisions are dominant on the macroscale.

Klein, L. W.↗
NASA NTRS1987

Microphysics of the auroral acceleration region of other regions of the magnetosphere

Electric field and plasma measurements pertinent to the microphysics of the auroral acceleration region are reviewed. Observations in other regions of the magnetosphere, which appear to involve similar physical processes, are summarized in order to emphasize the requirement on Cluster instrumentation for wide dynamic range, high time resolution, time domain field, and particle measurements. It is suggested that the microphysics of current driven instabilities in the auroral acceleration region is duplicated in the high latitude boundary of the plasma sheet and that the macroscale structure of the tail is determined by this microphysics.

Mozer, F. S.↗
NASA NTRS1988

Vapor condensation rate at a turbulent liquid interface, for application to cryogenic hydrogen

The condensation of hydrogen vapor onto turbulent liquid hydrogen is simulated experimentally using steam and water at elevated pressure, where water has a Prandtl number comparable to that of liquid hydrogen. A correlation is presented for the condensation rate in terms of the intensity and macroscale of the turbulence on the liquid side. The rate correlation should be applicable to low-gravity conditions at the higher turbulence intensities; at the lower turbulence intensities, however, the data are affected by thermal stratification resulting from buoyancy effects.

Helmick, M. R.↗
NASA NTRS1987

Evaluating North American net primary productivity with satellite observations

An ecological model is developed to estimate annual net primary productivity (NPP) in 12 North American biomes. The model combines existing models which address canopy photosynthesis in response to light, temperature, and moisture availability, and account for respiration. Climate data, solar radiation data, and spectral vegetation index data are utilized. Estimates of NPP from the model compare well with data in the literature, but a systematic error is suspected. Difficulties encountered in specifying certain model parameters are discussed as possible sources of this error. The results of this study suggest the promise of remotely sensed measurements for macroscale evaluation and modeling of NPP.

Goward, Samuel N.↗
NASA NTRS1987

Dynamic crystallization experiments on chondrule melts in reduced gravity

Chondrules crystallized during the earliest formational history of the solar system; and, if crystal settling and flotation are indicators of crystallization in the presence of gravity, they formed without the influence of gravity. In fact, attempts to duplicate the crystallization history of chondrules in the laboratory have met with limited success, because of the difficulty of comparing objects formed under the influence of gravity with objects that did not. These comparisons are difficult because there are several recognized features introduced by the presence of gravity and no doubt some which are not yet recognized. As a result there are several microscale and macroscale aspects of chondrule petrology which are difficult to understand quantitatively. Most of the features relate to the settling or flotation of early formed crystals. The proposed experiments are briefly described.

Lofgren, Gary↗
NASA NTRS1989

Excitation of kinetic Alfven waves by resonant mode conversion and longitudinal heating of magnetized plasmas

The excitation of the kinetic Alfven wave by resonant mode conversion and longitudinal heating of the plasma by the kinetic Alfven wave were demonstrated on the basis of a macroscale particle simulation. The longitudinal electron current was shown to be cancelled by the ions. The kinetic Alfven wave produced an ordered motion of the plasma particles in the wave propagation direction. The electrons were pushed forward along the ambient magnetic field by absorbing the kinetic Alfven wave through the Landau resonance.

Tanaka, Motohiko↗
NASA NTRS1989

Satellite bioclimatology

Satellite-acquired, remotely sensed observations of the earth's land areas are substantially advancing knowledge of global vegetation patterns. Recognition that combined visible/near infrared spectral reflectance observations are a general indicator of the presence, condition and magnitude of vegetation foliage provides a basis for explanation. This information is of considerable value in climatic research because of the links between climate variables and vegetation foliage. Presence of vegetation foliage is predominantly determinated by a combination of local heat and moisture conditions. In turn, foliar presence determines local rates of photosynthesis, affects surface albedo, and influences local rates of evapotranspiration as well as other elements of surface energy/mass balance. Availability of these remotely sensed data provides, for the first time, a consistent, global means to directly study interactions between climate and vegetation. This understanding is now being incorporated in climatological research and should improve understanding of macroscale bioclimatology. Remote sensing technology and understanding of this technology are continuing to develop rapidly and further major advances in this new field of'satellite bioclimatology' can be expected in the near future.

Goward, Samuel N.↗
NASA NTRS1990

Comparison of SSM/I measurements to numerically-simulated cloud and precipitation during ERICA

These investigations focused essentially on the macroscale organization of cloud and precipitation which occurred during the 4th Intensive Observing Period (IOP-4) of the Experiment for Rapidly Intensifying Cyclones over the Atlantic (ERICA). This experiment, held off the East Coast of the United States and Canada during the winter of 1989, documented several episodes of rapid cyclonic storm development. Also playing a major role as validation and ground truth in these studies are Special Sensor Microwave Imager (SSM/I) retrievals of precipitable water, total liquid water and ice, generated by other Marshall Space Flight Center (MSFC) supported investigations. Model simulations produced to date suggest that, while the large-scale atmospheric dynamics was an essential driving mechanism, the role of condensation was crucial in facilitating the exceptionally rapid spinup of the cyclone and the low surface pressure. A model simulation of the precipitation rate at the time of most rapid storm intensification is shown in the accompanying figure. Heavier precipitation rates in the crescent shaped region are associated with deep convection along the leading edge of a dry intrusion behind the surface low. The majority of precipitation in the stratiform region to the northeast involved the production of ice with deposition from vapor to ice being the dominant process of growth. Some small amount of mixed phase cloudiness was present. Model condensate distributions matched well with SSM/I observations. The accompanying SSM/I imagery which delineates areas of large (greater than several hundred micron effective radius) precipitating ice over the ocean suggests that the model has done well in capturing the essential mechanisms responsible for the horizontal distribution of precipitation.

Robertson, Franklin R.↗
NASA NTRS1990

Water balance model for Kings Creek

Particular attention is given to the spatial variability that affects the representation of water balance at the catchment scale in the context of macroscale water-balance modeling. Remotely sensed data are employed for parameterization, and the resulting model is developed so that subgrid spatial variability is preserved and therefore influences the grid-scale fluxes of the model. The model permits the quantitative evaluation of the surface-atmospheric interactions related to the large-scale hydrologic water balance.

Wood, Eric F.↗
NASA NTRS1992

Mixing in the dome region of a staged gas turbine combustor

To lower NO(x) emissions from gas-turbine engines the effect of dome design and operational changes on the mixing quality in the fuel-rich region is studied. A statistical analysis is employed to establish the parametric sensitivity in this complex flow. A mixing-effectiveness index is defined and used to optimize the gas-species uniformity and the extent of reaction at the exit plane of the dome. Mixing effectiveness is tied to the fuel and air injection locations, the macroscale structure of the dome aerodynamics, and the level of turbulence. Increases in nozzle/air to fuel ratio, reference velocities, and the dome expansion angle increased the level of turbulence. The optimum configuration featured counter-swirling fuel and air streams and produced a strong torroidal recirculation zone, an effective spray angle of 45 degrees, and azimuthal velocities that decayed to zero inside of two duct diameters. The results underscore the system specific nature of mixing optimization.

Sowa, W. A.↗
NASA NTRS1992

Scalar rate correlation at a turbulent liquid free surface - A two-regime correlation for high Schmidt numbers

An experimental correlation is derived for gas absorption at a turbulent, shear-free liquid interface. The correlation is expressed in terms of the liquid-side turbulence intensity, liquid-side macroscale, and the properties of the diffusing gas and solvent. The transfer coefficient increases linearly with rms velocity up to a point where the eddy Reynolds number reaches a critical (Schmidt number dependent) value. At higher velocities, there is a more rapid linear rise. The slope of the lower Reynolds number region is proportional to the square root of the diffusivity; at Reynolds numbers much higher than that of the break point, the slope becomes independent of diffusivity.

Khoo, Boo-Cheong↗