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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Experimental study on optimization parameters of a supersonic jet ejector thrust augmentor.

The experimental data were aimed at obtaining the effect of jet mixing, the effective length/diameter of the ejector tube, the entrance length shape factor, the shape loading, and the optimum primary jet location. The total augmented thrust is proportional to the diameter of the ejector. The data show that for a practical design the entrance lip shape and the stream lines around the lip are also important in order to optimize the percentage augmentation.

Cheng, D. Y.↗
NASA NTRS1974

Correlation parameters for the study of leeside heating on a lifting body at hypersonic speeds

Leeside heating was studied with the aim of gaining some insight into: (1) the magnitude of the leeside heating rates and (2) the methods to be used to extrapolate wind tunnel leeside heating rates to the full scale flight condition. This study was based on existing experimental data obtained in a hypersonic shock tunnel on lifting body configurations that are typical of shuttle orbiter vehicles. Heat transfer was first measured on the windward side to determine the boundary layer type. Then the leeside heating was investigated with the classified boundary layer. Correlation data are given on the windward turbulent boundary layer, the windward laminar boundary layer, and the leeside surfaces.

Vidal, R. J.↗
NASA NTRS1978

Analytical techniques for the study of some parameters of multispectral scanner systems for remote sensing

The author has identified the following significant results. The concept of average mutual information in the received spectral random process about the spectral scene was developed. Techniques amenable to implementation on a digital computer were also developed to make the required average mutual information calculations. These techniques required identification of models for the spectral response process of scenes. Stochastic modeling techniques were adapted for use. These techniques were demonstrated on empirical data from wheat and vegetation scenes.

Wiswell, E. R.↗
NASA NTRS1983

An ISEE 3 high time resolution study of interplanetary parameter correlations with magnetospheric activity

The coupling between the solar wind and the geomagnetic disturbances was examined using data from the ISEE-3 spacecraft at an earth-sun libration point and ground-based data. One minute data were used to avoid aliasing in determining the internal magnetospheric response to solar wind conditions. Attention was given to the cross-correlations between the geomagnetic index (AE), the total energy dissipation rate (UT), and the solar wind parameters, as well as the spatial and temporal scales on which the magnetosphere reacts to the solar wind conditions. It was considered necessary to characterize the physics of the solar wind-magnetosphere coupling in order to define the requirements for a spacecraft like the ISEE-3 that could be used as a real time monitoring system for predicting storms and substorms. The correlations among all but one parameter were lower during disturbance intervals; UT was highly correlated with all parameters during the disturbed times. An intrinsic 25-40 min delay was detected between interplanetary activity and magnetospheric response in quite times, diminishing to no more than 15 min during disturbed times.

Baker, D. N.↗
NASA NTRS1984

Landsat image registration - A study of system parameters

Some applications of Landsat data, particularily agricultural and forestry applications, require the ability to geometrically superimpose or register data acquired at different times and possibly by different satellites. An experimental investigation relating to a registration processor used by the Johnson Space Center for this purpose is the subject of this paper. Correlation of small subareas of images is at the heart of this registration processor and the manner in which various system parameters affect the correlation process is the prime area of investigation. Parameters investigated include preprocessing methods, methods for detecting sucessful correlations, fitting a surface to the correlation patch, fraction of pixels designated as edge pixels in edge detection adn local versus global generation of edge images. A suboptimum search procedure is used to find a good parameter set for this registration processor.

Wacker, A. G.↗
NASA NTRS1988

Radial velocity studies and absolute parameters of contact binaries. I - AB Andromedae

New radial velocity curves have been obtained for the contact binary AB And, using the cross-correlation technique. A mass ratio of 0.479 is determined, which is revised to 0.491 when the velocities are corrected for proximity effects using a light curve model. These values differ by less than ten percent from the photometric mass ratio. An analysis of the symmetric B and V light curves reported by Rigterink in 1973 using the spectroscopic mass ratio yields a consistent set of light and velocity curve elements. These also produce a reasonably good fit to the infrared J and K light curves reported by Jameson and Akinci in 1979. Absolute elements are determined, and these indicate that both components have a main-sequence internal structure. These absolute parameters, together with the Galactic kinematics, suggest an age for the system similar to or greater than that of the Sun.

Hrivnak, Bruce J.↗
NASA NTRS1990

Spacelab 2 electron beam wave stimulation - Studies of important parameters

Experimental results from Spacelab 2 experiments on the production of waves in ionospheric plasma by the injection of pulsed electron beams are reported. The wave environments which exist in the orbiter payload bay and at several hundred meters away are compared both during ambient conditions and during electron beam injections. The duty cycle of the beam is found to be one of the most important parameters affecting the amplitude and the harmonic structure of the waves. Maximum amplitudes are produced by 50 percent duty cycles and amplitudes are proportional to instantaneous, rather than average, beam current. The dependence of the harmonic structure on pulsing frequency shows good agreement with theory for whistler mode waves produced by the Cerenkov resonance.

Reeves, G. D.↗
NASA NTRS1991

A comparative study of performance parameters of n(+)-p InP solar cells made by closed-ampoule sulfur diffusion into Cd- and Zn-doped p-type InP substrates

Preliminary results indicate that Cd-doped substrates are better candidates for achieving high efficiency solar cells fabricated by closed-ampoule sulfur (S) diffusion than Zn-doped substrates. The differences in performance parameters (i.e., 14.3 percent efficiency for Cd-doped vs. 11.83 percent in the case of Zn-doped substrates of comparable doping and etch pit densities) were explained in terms of a large increase in dislocation density as a result of S diffusion in the case of Zn-doped as compared to Cd-doped substrates. The In(x)S(y) and probably Zn(S) precipitates in the case of Zn-doped substrates, produce a dead layer which extends deep below the surface and strongly affects the performance parameters. It should be noted that the cells had an unoptimized single layer antireflective coating of SiO, a grid shadowing of 6.25 percent, and somewhat poor contacts, all contributing to a reduction in efficiency. It is believed that by reducing the external losses and further improvement in cell design, efficiencies approaching 17 percent at 1 AMO, 25 degrees should be possible for cells fabricated on these relatively high defect density Cd-doped substrates. Even higher efficiencies, 18 to 19 percent should be possible by using long-lifetime substrates and further improving front surface passivation. If solar cells fabricated on Cd-doped substrates turn out to have comparable radiation tolerance as those reported in the case of cells fabricated on Zn-doped substrates, then for certain space missions 18 to 19 percent efficient cells made by this method of fabrication would be viable.

Faur, Mircea↗
NASA NTRS1990

Tunable far infrared studies of molecular parameters in support of stratospheric measurements

The purpose of this research is to make precise, fully line-resolved measurements of molecular parameters that are necessary for the analysis of spectra obtained in far infrared field measurement programs. These measurements make it possible to accurately analyze the data from field measurements to obtain atmospheric concentration profiles of key trace gases involved in the ozone chemistry. The research objectives include: measurements of pressure broadening of molecular lines of OH, O2, O3, HCl, and H2O, their temperature dependence, and, when possible, the pressure-induced frequency shifts of the lines; measurements of line positions of radical species, such as HO2.

Chance, K. V.↗
NASA NTRS1992

Effects of clouds on the Earth radiation budget; Seasonal and inter-annual patterns

Seasonal and regional variations of clouds and their effects on the climatological parameters were studied. The climatological parameters surface temperature, solar insulation, short-wave absorbed, long wave emitted, and net radiation were considered. The data of climatological parameters consisted of about 20 parameters of Earth radiation budget and clouds of 2070 target areas which covered the globe. It consisted of daily and monthly averages of each parameter for each target area for the period, Jun. 1979 - May 1980. Cloud forcing and black body temperature at the top of the atmosphere were calculated. Interactions of clouds, cloud forcing, black body temperature, and the climatological parameters were investigated and analyzed.

Dhuria, Harbans L.↗
NASA NTRS1992

Parameter and configuration study of the DSS-13 antenna drives

The effects of different elevation and azimuth drive configurations on DSS-13 antenna performance are presented as well as a study of gearbox stiffness and motor inertia. Small motor inertia and rigid gearboxes would improve the pointing accuracy up to a certain limit. The limit is imposed by critical values of gearbox stiffness and motor inertia introduced in the article. The critical values depend on the lowest structural frequency of the rate-loop model. The tracking performance can be improved by raising gearbox stiffness to the critical stiffness and reducing motor inertia to the critical inertia. An azimuth drive configuration with four driven wheels was also investigated. For the four-wheel drive configuration in azimuth, the cross-coupling effects are reduced and wind disturbance rejection properties improved. Pointing is improved substantially in the cross-elevation but is relatively unaffected in the elevation direction. More significant improvements can be achieved through either structural redesign (stiffening the structure) or new control algorithms or control concepts, which would eliminate the effect of flexible deformations on the antenna pointing accuracy. Although the study is performed for the DSS-13 antenna, the results can be extended for other DSN antennas.

Gawronski, W.↗
NASA NTRS2001

Maximum Likelihood Estimation of the Broken Power Law Spectral Parameters with Detector Design Applications

The maximum likelihood procedure is developed for estimating the three spectral parameters of an assumed broken power law energy spectrum from simulated detector responses and their statistical properties investigated. The estimation procedure is then generalized for application to real cosmic-ray data. To illustrate the procedure and its utility, analytical methods were developed in conjunction with a Monte Carlo simulation to explore the combination of the expected cosmic-ray environment with a generic space-based detector and its planned life cycle, allowing us to explore various detector features and their subsequent influence on estimating the spectral parameters. This study permits instrument developers to make important trade studies in design parameters as a function of the science objectives, which is particularly important for space-based detectors where physical parameters, such as dimension and weight, impose rigorous practical limits to the design envelope.

Howell, Leonard W.↗
DOE OSTI2025

Quality Guidelines for Energy System Studies: Process Modeling Design Parameters

The National Energy Technology Laboratory (NETL) conducts systems analysis studies that require a large number of inputs, from ambient conditions to parameters for Aspen Plus ® (Aspen) process blocks. The sheer number of assumptions required makes it impractical to document all of them in each issued report. The purpose of the Quality Guidelines for Energy System Studies (QGESS) is to document the assumptions most commonly used in system analysis studies and the basis for those assumptions. In order to develop the systems analysis models presented in various NETL reports, significant vendor data have been obtained, and these data enhance the model outputs. Much of the vendor data obtained are considered proprietary and not suitable for public release or attribution to a specific vendor. As such, several sub-systems common in NETL reports and their process parameter data are not reported in this document to protect proprietary vendor information. The values and ranges of values presented in this report represent assumptions that have been made in previous studies.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1976

An empirical study of scanner system parameters

The selection of the current combination of parametric values (instantaneous field of view, number and location of spectral bands, signal-to-noise ratio, etc.) of a multispectral scanner is a complex problem due to the strong interrelationship these parameters have with one another. The study was done with the proposed scanner known as Thematic Mapper in mind. Since an adequate theoretical procedure for this problem has apparently not yet been devised, an empirical simulation approach was used with candidate parameter values selected by the heuristic means. The results obtained using a conventional maximum likelihood pixel classifier suggest that although the classification accuracy declines slightly as the IFOV is decreased this is more than made up by an improved mensuration accuracy. Further, the use of a classifier involving both spatial and spectral features shows a very substantial tendency to resist degradation as the signal-to-noise ratio is decreased. And finally, further evidence is provided of the importance of having at least one spectral band in each of the major available portions of the optical spectrum.

Landgrebe, D.↗
NASA NTRS2010

Selection Effects in Identifying Magnetic Clouds and the Importance of the Closest Approach Parameter

This study is motivated by the unusually low number of magnetic clouds (MCs) that are strictly identified within interplanetary coronal mass ejections (ICMEs), as observed at 1 AU; this is usually estimated to be around 30% or lower. But a looser definition of MCs may significantly increase this percentage. Another motivation is the unexpected shape of the occurrence distribution of the observers' "closest approach distances" (measured from a MC's axis, and called CA) which drops off somewhat rapidly as |CA| (in % of MC radius) approaches 100%, based on earlier studies. We suggest, for various geometrical and physical reasons, that the |CA|-distribution should be somewhere between a uniform one and the one actually observed, and therefore the 30% estimate should be higher. So we ask, When there is a failure to identify a MC within an ICME, is it occasionally due to a large |CA| passage, making MC identification more difficult, i.e., is it due to an event selection effect? In attempting to answer this question we examine WIND data to obtain an accurate distribution of the number of MCs vs. |CA| distance, whether the event is ICME-related or not, where initially a large number of cases (N=98) are considered. This gives a frequence distribution that is far from uniform, confirming earlier studies. This along with the fact that there are many ICME identification-parameters that do not depend on |CA| suggest that, indeed an MC event selection effect may explain at least part of the low ratio of (No. MCs)/(No. ICMEs). We also show that there is an acceptable geometrical and physical consistency in the relationships for both average "normalized" magnetic field intensity change and field direction change vs. |CA| within a MC, suggesting that our estimates of |CA|, B(sub 0) (magnetic field intensity on the axis), and choice of a proper "cloud coordinate" system (all needed in the analysis) are acceptably accurate. Therefore the MC fitting model (Lepping et al., 1990) is adequate, on average, for our analysis. However, this selection effect is not likely to completely answer our original question, on the unexpected ratio of MCs to ICMEs, so we must look for other factors, such as peculiarities of CME birth conditions. As a by-product of this analysis, we determine that the first order structural effects within a MC due to its interaction with the solar wind, plus the MC's usual expansion at 1 AU (i.e., the non-force free components of the MC's field) are, on average, weakly dependent on radial distance from the MC's axis; that is, in the outer reaches of a typical MC the non-force free effects show up, but even there they are rather weak. Finally, we show that it is not likely that a MC's size distribution statistically controls the occurrence distribution of the estimated |CA|s.

Lepping, R. P.↗