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Results for “prior knowledge”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The utility of surface temperature measurements for the remote sensing of surface soil water status

Experiments carried out on an Avondale loam soil indicated that the thermal inertia concept of soil water content detection is reasonably sound. The volumetric water contents of surface soil layers between 2 and 4 cm thick were found to be linear functions of the amplitude of the diurnal surface soil temperature wave for clear day-night periods. They were also found to be linear functions of the daily maximum value of the surface soil-air-temperature differential. Tests on three additional soils ranging from sandy loam to clay indicated that the relations determined for Avondale loam could not be accurately applied to these other soil types. When the moisture characteristic curves of each soil were used to transform water contents into pressure potentials, however, it was found that soil water pressure potential could be determined without prior knowledge of soil type, and thus its value as a potential soil water status survey tool was significantly enhanced.

Idso, S. B.↗
NASA NTRS1976

The concept verification testing of materials science payloads

The concept Verification Testing (CVT) project at the Marshall Space Flight Center, Alabama, is a developmental activity that supports Shuttle Payload Projects such as Spacelab. It provides an operational 1-g environment for testing NASA and other agency experiment and support systems concepts that may be used in shuttle. A dedicated Materials Science Payload was tested in the General Purpose Laboratory to assess the requirements of a space processing payload on a Spacelab type facility. Physical and functional integration of the experiments into the facility was studied, and the impact of the experiments on the facility (and vice versa) was evaluated. A follow-up test designated CVT Test IVA was also held. The purpose of this test was to repeat Test IV experiments with a crew composed of selected and trained scientists. These personnel were not required to have prior knowledge of the materials science disciplines, but were required to have a basic knowledge of science and the scientific method.

Griner, C. S.↗
NASA NTRS1977

Chain Pooling modeling selection as developed for the statistical analysis of a rotor burst protection experiment

As many as three iterated statistical model deletion procedures were considered for an experiment. Population model coefficients were chosen to simulate a saturated 2 to the 4th power experiment having an unfavorable distribution of parameter values. Using random number studies, three model selection strategies were developed, namely, (1) a strategy to be used in anticipation of large coefficients of variation, approximately 65 percent, (2) a strategy to be sued in anticipation of small coefficients of variation, 4 percent or less, and (3) a security regret strategy to be used in the absence of such prior knowledge.

Holms, A. G.↗
NASA NTRS1978

Application of the laser velocimeter to airfoil research

A laser velocimeter (LV) was installed in the Langley V/STOL tunnel to measure the velocity field about a wing with a NACA 0012 airfoil section. These measurements were compared at low angle of attack with a two dimensional, viscous flow prediction program. The velocity field over the wing in a fully stalled condition was also measured by the LV. The unique ability of the LV to measure absolute flow magnitude and direction without prior knowledge of general flow direction was demonstrated in the complex separated reverse flows near the wing upper surface at the high angle of attack. The general characteristics of the flow field over the stalled wing were substantiated by a vapor screen flow visualization technique.

Hoad, D. R.↗
NASA NTRS1980

Optical calibrator for TDL spectrometers

Two etalons and monochromator mode selector help calibrate spectrometer in selected laser mode. Technique accurately determines free spectral range of etalon. By establishing number of fringes between two modes, both of which have been calibrated with molecular line standards, one finds free spectral range with error inversely proportional to spectral interval between calibration points. Procedure establishes free spectral range of etalon without prior knowledge of its length or refractive index.

Jennings, D. E.↗
NASA NTRS1980

'Chain pooling' model selection for two-level fixed effects factorial experiments

As many as three iterated statistical model deletion procedures are considered for an experiment. Population model coefficients were chosen to simulate a saturated factorial experiment having an unfavorable distribution of parameter values. Using random number studies, three model selection strategies were developed, namely, (1) a strategy to be used in anticipation of large coefficients of variation (neighborhood of 65 percent), (2) strategy to be used in anticipation of small coefficients of variation (4 percent or less), and (3) a security regret strategy to be used in the absence of such prior knowledge.

Holms, A. G.↗
NASA NTRS1980

Use of a Helmholtz burner for low frequency velocity coupled instability measurements

The low frequency velocity coupled response of a composite propellant during combustion was investigated using a Helmholtz resonator in the burner which results in a 230 Hz natural frequency in a chamber less than 30 inches long. Experiments indicate that the acoustic characteristics of the burner permit determination of propellant velocity coupled without prior knowledge of pressure coupled response. Comparisons of burner data and full scale motor firings confirm the ability of the burner to rank propellants for their velocity coupling tendencies. The burner design rationale is described and experimental results are presented.

Lyon, J. M.↗
NASA NTRS1980

ICAP: An Interactive Cluster Analysis Procedure for analyzing remotely sensed data

An Interactive Cluster Analysis Procedure (ICAP) was developed to derive classifier training statistics from remotely sensed data. The algorithm interfaces the rapid numerical processing capacity of a computer with the human ability to integrate qualitative information. Control of the clustering process alternates between the algorithm, which creates new centroids and forms clusters and the analyst, who evaluate and elect to modify the cluster structure. Clusters can be deleted or lumped pairwise, or new centroids can be added. A summary of the cluster statistics can be requested to facilitate cluster manipulation. The ICAP was implemented in APL (A Programming Language), an interactive computer language. The flexibility of the algorithm was evaluated using data from different LANDSAT scenes to simulate two situations: one in which the analyst is assumed to have no prior knowledge about the data and wishes to have the clusters formed more or less automatically; and the other in which the analyst is assumed to have some knowledge about the data structure and wishes to use that information to closely supervise the clustering process. For comparison, an existing clustering method was also applied to the two data sets.

Wharton, S. W.↗
NASA NTRS1980

Backward deletion to minimize prediction errors in models from factorial experiments with zero to six center points

Population model coefficients were chosen to simulate a saturated 2 to the 4th fixed-effects experiment having an unfavorable distribution of relative values. Using random number studies, deletion strategies were compared that were based on the F-distribution, on an order statistics distribution of Cochran's, and on a combination of the two. The strategies were compared under the criterion of minimizing the maximum prediction error, wherever it occurred, among the two-level factorial points. The strategies were evaluated for each of the conditions of 0, 1, 2, 3, 4, 5, or 6 center points. Three classes of strategies were identified as being appropriate, depending on the extent of the experimenter's prior knowledge. In almost every case the best strategy was found to be unique according to the number of center points. Among the three classes of strategies, a security regret class of strategy was demonstrated as being widely useful in that over a range of coefficients of variation from 4 to 65%, the maximum predictive error was never increased by more than 12% over what it would have been if the best strategy had been used for the particular coefficient of variation. The relative efficiency of the experiment, when using the security regret strategy, was examined as a function of the number of center points, and was found to be best when the design used one center point.

Holms, A. G.↗
NASA NTRS1980

Resolving the percentage of component terrains within single resolution elements

An approximate maximum likelihood technique employing a widely available discriminant analysis program is discussed that has been developed for resolving the percentage of component terrains within single resolution elements. The method uses all four channels of Landsat data simultaneously and does not require prior knowledge of the percentage of components in mixed pixels. It was tested in five cases that were chosen to represent mixtures of outcrop, soil and vegetation which would typically be encountered in geologic studies with Landsat data. For all five cases, the method proved to be superior to single band weighted average and linear regression techniques and permitted an estimate of the total area occupied by component terrains to within plus or minus 6% of the true area covered. Its major drawback is a consistent overestimation of the pixel component percent of the darker materials (vegetation) and an underestimation of the pixel component percent of the brighter materials (sand).

Marsh, S. E.↗
NASA NTRS1983

A one-dimensional unsteady model of dual mode scramjet operation

A one-dimensional unsteady model and code have been developed which can handle internal flows involving area change, heat release, transients and coupled inviscid core-boundary layer flows. The model has been shown to work well in diverging channels with a supersonic entrance Mach number and unseparated boundary layers. Transient flows have also been studied. The model needs no prior knowledge of shock (or shocks) location and can be extended to two or three dimensions. The results show that the one-dimensional unsteady model developed here can be used for analysis of internal flows as occur in scramjet combustors.

Bussing, T. R. A.↗
NASA NTRS1984

In-trail dynamics of multiple CDTI-equipped aircraft queues

One of the potential problems of in-trail self-spacing with a Cockpit Display of Traffic Information (CDTI) is whether dynamic oscillations would occur in a queue of aircraft flying an approach, similar to the ""accordion'' effect seem with the queue of automobiles in stop-and-go traffic. In order to gain some insight into this potential problem, a brief experiment was conducted with the Transport Systems Research Vehicle (TSRV) ground-based simulator equipped with CDTI which presented the position of other aircraft in the area. Three simulation sessions were conducted wherein queues of up to nine aircraft were built, each one self-spacing on the preceding aircraft. The aircraft crews were rotated to ensure that the pilots had no prior knowledge of the lead aircraft behavior they would be following. Two different spacing criteria were employed: a constant time predictor criterion and a constant time delay criterion. The experiment failed to uncover any dynamic oscillatory tendencies in queues of seven to nine aircraft.

Kelly, J. R.↗
NASA NTRS1983

Restriction of pursuit eye movement range during a concurrent auditory task

A two-part experiment was performed using 10 naive adult male subjects to determine the effects of a concurrent auditory dot/dash identification task on pursuit eye movements. Results indicated there was a significant (20 percent) but transitory task-induced restriction of the range of both an 18 deg horizontal and a 14 deg vertical pursuit eye movement visual angle. Furthermore, doubling the presentation rate of the concurrent task accounted for an additional 5 percent restriction of pursuit eye movement range. Results also indicated that the eye movement range is unaffected by both prior knowledge of the task and four consecutive practice trials. It is suggested that both the rapidity of target movement and the presence of concurrent mental tasks could significantly shrink an operator's pursuit eye movement ranges during viewing of dynamic visual displays such as airborne low-level television and forward-looking infrared.

Malmstrom, F. V.↗
NASA NTRS1984

A Full Mission Simulator Study of Aircrew Performances: the Measurement of Crew Coordination and Decisionmaking Factors and Their Relationships to Flight Task Performances

Sixteen three man crews flew a full mission scenario in an airline flight simulator. A high level of verbal interaction during instances of critical decision making was located. Each crew flew the scenario only once, without prior knowledge of the scenario problem. Following a simulator run and in accord with formal instructions, each of the three crew members independently viewed and commented on a videotape of their performance. Two check pilot observers rated pilot performance across all crews and, following each run, also commented on the video tape of the crew's performance. A linguistic analysis of voice transcript is made to provide assessment of crew coordination and decision making qualities. Measures of crew coordination and decision making factors are correlated with flight task performance measures.

Murphy, M. R.↗
NASA NTRS1987

Analyzing Nonisothermal Crystallization of Thermoplastics

Method developed for analysis of nonisothermal cold crystallization in thermoplastics. Does not require prior knowledge of isothermal kinetic parameters. Based upon observation: During nonisothermal crystallization at constant rate, relative crystallinity develops with time dependence sigmoidal at low degrees of conversion. Application for method is study of cold crystallization in advanced thermoplastics.

Cebe, Peggy↗
NASA NTRS1986

Application of the cepstrum to remove echoes from rotor acoustic spectra

The application of the power cepstrum technique to the analysis of model scale helicopter rotor noise spectra is investigated. The power cepstrum technique emerges as a useful tool for the removal of undesired acoustic reflections from measured rotor spectra. It is most effective when the reflections are exact duplicates of the signal, i.e., when the echo transfer function is linear. Moreover, the technique is best applied to a measured spectrum which is due entirely to the signal and its echoes, when no nonsource related signals are present. It is noted that this technique can be applied without prior knowledge of the echo characteristics.

Martin, R. M.↗
NASA NTRS1987

Estimation of local spatial scale

The concept of local scale asserts that for a given class of psychophysical measurements, performance at any two visual field locations is equated by magnifying the targets by the local scale associated with each location. Local scale has been hypothesized to be equal to cortical magnification or alternatively to the linear density of receptors or ganglion cells. Here, it is shown that it is possible to estimate local scale without prior knowledge about the scale or its physiological basis.

Watson, Andrew B.↗
NASA NTRS1990

Measuring Diameters Of Large Vessels

Computerized apparatus produces accurate results quickly. Apparatus measures diameter of tank or other large cylindrical vessel, without prior knowledge of exact location of cylindrical axis. Produces plot of inner circumference, estimate of true center of vessel, data on radius, diameter of best-fit circle, and negative and positive deviations of radius from circle at closely spaced points on circumference. Eliminates need for time-consuming and error-prone manual measurements.

Currie, James R.↗