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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 523 records · Page 29

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NASA NTRS1989

Characterization of a thermally imidized soluble polyimide film

A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids).

Young, Philip R.↗

NASA NTRS1990

Characterization of a thermally imidized soluble polyimide film

Young, Philip R.↗

NASA NTRS1990

Experiments on a separation bubble over an Eppler 387 airfoil at low Reynolds numbers using thin-film arrays

Experiments carried out at the NASA Langley Low-Turbulence Pressure Tunnel on an Eppler 387 airfoil at several angles of attack for Reynolds numbers of 100,000 to 300,000 are discussed. Cross-correlations and phase diagrams are used in calculating velocities, while spectra are used in checking for amplified frequencies, and coherence plots for causality. Hot-film measurements, oil-flow visualization, pressure measurements, and Drela code are compared for finding the leading and trailing edges of the bubble. It is observed that all methods agree in showing the beginning and end of the separation bubble, the velocity measurements agree in magnitude for the lower velocities, and wave packets appear in the cross-correlation.

Mousseux, Marc C.↗

NASA NTRS1991

Display format, highlight validity, and highlight method: Their effects on search performance

Display format and highlight validity were shown to affect visual display search performance; however, these studies were conducted on small, artificial displays of alphanumeric stimuli. A study manipulating these variables was conducted using realistic, complex Space Shuttle information displays. A 2x2x3 within-subjects analysis of variance found that search times were faster for items in reformatted displays than for current displays. Responses to valid applications of highlight were significantly faster than responses to non or invalidly highlighted applications. The significant format by highlight validity interaction showed that there was little difference in response time to both current and reformatted displays when the highlight validity was applied; however, under the non or invalid highlight conditions, search times were faster with reformatted displays. A separate within-subject analysis of variance of display format, highlight validity, and several highlight methods did not reveal a main effect of highlight method. In addition, observed display search times were compared to search time predicted by Tullis' Display Analysis Program. Benefits of highlighting and reformatting displays to enhance search and the necessity to consider highlight validity and format characteristics in tandem for predicting search performance are discussed.

Donner, Kimberly A.↗

NASA NTRS1992

Application of vector-valued rational approximations to the matrix eigenvalue problem and connections with Krylov subspace methods

Let F(z) be a vectored-valued function F: C approaches C sup N, which is analytic at z=0 and meromorphic in a neighborhood of z=0, and let its Maclaurin series be given. We use vector-valued rational approximation procedures for F(z) that are based on its Maclaurin series in conjunction with power iterations to develop bona fide generalizations of the power method for an arbitrary N X N matrix that may be diagonalizable or not. These generalizations can be used to obtain simultaneously several of the largest distinct eigenvalues and the corresponding invariant subspaces, and present a detailed convergence theory for them. In addition, it is shown that the generalized power methods of this work are equivalent to some Krylov subspace methods, among them the methods of Arnoldi and Lanczos. Thus, the theory provides a set of completely new results and constructions for these Krylov subspace methods. This theory suggests at the same time a new mode of usage for these Krylov subspace methods that were observed to possess computational advantages over their common mode of usage.

Sidi, Avram↗

NASA NTRS1991

The application of time-dependent wavepacket methods to reactive scattering

Several methods for performing numerically exact reactive scattering calculations using time-dependent wavepackets are reviewed. The basic idea is to take the multiarrangement reactive problem and reformulate it as one or more inelastic ones. In the simplest method, total reaction probabilities are extracted by calculating the flux of the wavepacket as it leaves the interaction region in the direction of the reactive arrangement. To make this practical, complex potentials that absorb the wavepacket before it reaches the numerical grid boundary are used. Methods that generate observables ranging from total, energy-averaged reaction probabilities up to energy- and state-resolved S-matrix elements are used. Techniques for efficiently performing the necessary inelastic wavepacket propagation are also reviewed.

Neuhauser, Daniel↗

NASA NTRS1992

The effects of small ice crystals on cirrus infrared radiative properties

Using a model that combines single-scattering properties for spheroidal and hexagonal ice crystals, the thermal infrared radiative properties of cirrus clouds have been investigated. Infrared scattering and absorption properties for randomly oriented spheroids and hexagons are parameterized based on the anomalous diffraction theory and a geometric ray-tracing method, respectively. Using observed ice crystal size distributions, upwelling radiances at the top of cirrus cloudy atmospheres have been computed. Results show that the presence of small ice crystals can produce significant brightness temperature differences between two infrared wavelengths in the 10-micron window. Theoretical results have been compared with observed brightness temperature differences between 8.35 and 11.16 microns and between 11.16 and 12 microns. The observed values were obtained from the high-spectral resolution interferometer sounder. It is shown that the use of the present nonspherical model for ice crystals in radiative transfer calculations leads to a significantly better interpretation of the observed data than does the use of the spherical model.

Takano, Y.↗

NASA NTRS1993

Observational and modeling studies of heat, moisture, precipitation, and global-scale circulation patterns

The research sponsored by this grant is a continuation and an extension of the work conducted under a previous contract, 'South Pacific Convergence Zone and Global-Scale Circulations'. In the prior work, we conducted a detailed investigation of the South Pacific convergence zone (SPCZ), and documented many of its significant features and characteristics. We also conducted studies of its interaction with global-scale circulation features through the use of both observational and modeling studies. The latter was accomplished toward the end of the contract when Dr. James Hurrell, then a Ph.D. candidate, successfully ported the NASA GLA general circulation model (GCM) to Purdue University. In our present grant, we have expanded our previous research to include studies of other convectively-driven circulation systems in the tropics besides the SPCZ. Furthermore, we have continued to examine the relationship between these convective systems and global-scale circulation patterns. Our recent research efforts have focused on three objectives: (1) determining the periodicity of large-scale bands of organized convection in the tropics, primarily synoptic to intraseasonal time scales in the Southern Hemisphere; (2) examining the relative importance of tropical versus mid-latitude forcing for Southern Hemisphere summertime subtropical jets, particularly over the Pacific Ocean; and (3) estimating tropical precipitation, especially over oceans, using observational and budget methods. A summary list of our most significant accomplishments in the past year is given.

Vincent, Dayton G.↗

NASA NTRS1993

Application of hardness testing in foundry processing operations: A university and industry partnership

The objectives are the following: (1) to plan a tour of local manufacturing facility to observe hardness testing methods used and how they support the manufacturing process today; (2) to learn the operation of Brinell Hardness Testing and equipment set up with samples of accessory equipment for testing of various materials; (3) to use a Brinell scope (hand magnifier) to measure the diameter of the test indentation (in millimeters); (4) to use the hardness equation to determine the spherical area of the indentation and the calculation of the Brinell Hardness Number; (5) to use standard charts for ASTM standard size indenters to find the hardness number; and (6) to learn a method of conversion of the Brinell number to other hardness scales, their common usage, and also to convert the hardness number to the approximate tensile strength.

Martin, Donald H.↗

NASA NTRS1993

Optically thin cirrus clouds - Radiative impact on the warm pool

The role of the radiative effects of thin cirrus clouds in the energy balance of the 'warm pool' region is examined with reference to data obtained by the Infrared Interferometer Spectrometer (IRIS) flown on the Nimbus 4 satellite in 1970. First, the IRIS observations and a method for deriving the thin cirrus information are briefly discussed. A simple radiative energy balance model is then developed which is applicable to the mesoscale convective systems in the 'warm pool'. The radiative energy balance model, which does not explicitly account for the transports, is used to demonstrate the net radiative heating produced by the thin cirrus clouds.

Prabhakara, C.↗

NASA NTRS1936

Flow phenomena on plates and airfoils of short span

Investigations on the flow phenomena at plates and cambered models were carried out with the aid of force measurements, some pressure distribution measurements, and photographic observation. The experimental methods are described and the results given. Section III of this work gives a comprehensive account of the results and enables us to see how nearly the lift line and lift surface theories agree with the experimental results.

Winter, H↗

NASA NTRS1993

Remote visual detection of impacts on the lunar surface

We propose a novel method of remotely observing impacts on the airless Moon that may extend the present data base on meteoroids down to 1 m in diameter. Meteorites or comets of radius approximately 1-100 m are burnt away or dispersed in the atmospheres of the Earth and Venus. However, when such objects strike the Moon they deposit their energy in a small initial volume, forming a plasma plume whose visible and infrared radiation may be visible from the Earth. We consider impacts of model SiO2 projectiles on the surface of an SiO2 model Moon.

Melosh, H. Jay↗

NASA NTRS1995

Production of a long-term global water vapor and liquid water data set using ultra-fast methods to assimilate multi-satellite and radiosonde observations

There is a well-documented requirement for a comprehensive and accurate global moisture data set to assist many important studies in atmospheric science. Currently, atmospheric water vapor measurements are made from a variety of sources including radiosondes, aircraft and surface observations, and in recent years, by various satellite instruments. Creating a global data set from a single measuring system produces results that are useful and accurate only in specific situations and/or areas. Therefore, an accurate global moisture data set has been derived from a combination of these measurement systems. Under a NASA peer-reviewed contract, STC-METSAT produced two 5-yr (1988-1992) global data sets. One is the total column (integrated) water vapor data set and the other, a global layered water vapor data set using a combination of radiosonde observations, Television and Infrared Observation Satellite (TIROS) Operational Satellite (TOVS), and Special Sensor Microwave/Imager (SSM/I) data sets. STC-METSAT also produced a companion, global, integrated liquid water data set. The complete data set (all three products) has been named NVAP, an anachronym for NASA Water Vapor Project. STC-METSAT developed methods to process the data at a daily time scale and 1 x 1 deg spatial resolution.

Vonderhaar, Thomas H.↗

NASA NTRS1996

Interaction Dynamics Between a Flexible Rotor and an Auxiliary Clearance Bearing

This study investigates the application of synchronous interaction dynamics methodology to the design of auxiliary bearing systems. The technique is applied to a flexible rotor system and comparisons are made between the behavior predicted by this analysis method and the observed simulation response characteristics. Of particular interest is the influence of coupled shaft/bearing vibration modes on rotordynamical behavior. Experimental studies are also perFormed to validate the simulation results and provide insight into the expected behavior of such a system.

Lawen, James L., Jr.↗

NASA NTRS1993

Three-Dimensional Reconstruction of Asteroids from Radar Observations

A program of research has recently been initiated under the NASA Innovative Research Program to develop and test techniques for reconstructing the three-dimensional shapes of asteroids from ground-based radar observations. Presently, no methods exist to do this and the full scientific potential of current radar data sets lies untapped. The situation will become even more pronounced in approximately two years when the upgraded Arecibo radar system becomes capable of regularly producing asteroid data sets with very fine spatial resolution and high signal-to-noise ratios. If successful, the proposed research will significantly increase our knowledge of these objects. The potential and limitations of the techniques developed will be rigorously tested in a series of computer simulations and optical scattering experiments with scale models.

Hudson, Scott↗

NASA NTRS1997

A Novel Application of Ultrasonic Imaging to Study Smoldering Combustion

An ultrasonic imaging technique has been developed to examine the propagation of a smolder reaction within a porous combustible material. The technique provides information about the location of a propagating smolder front, as well as line-of-sight average permeability variations of the smoldering material. The method utilizes the observation that transmission of an ultrasonic signal through a porous material increases with permeability. Since a propagating smolder reaction leaves behind char with a higher permeability than the original material, ultrasound transmission can be employed to monitor smolder progress. The technique can also be used to track the char evolution as it continues to react. Experiments are presented where the technique is applied to smoldering combustion in a two-dimensional geometry. The results have furthered the understanding of two-dimensional smolder, especially in identifying the controlling mechanisms leading to the transition from smoldering to flaming. The applicability of ultrasonic tomography to smoldering combustion has also been investigated.

Tse, S. D.↗

NASA NTRS1998

Solar Irradiance and Thermospheric Airglow Rocket Experiments

This report describes work done in support of the Solar Irradiance and Thermospheric Air-glow Rocket Experiments at the University of Colorado for NASA grant NAG5-5021 under the direction of Dr. Stanley C. Solomon. (The overall rocket program is directed by Dr. Thomas N. Woods, formerly at the National Center for Atmospheric Research, and now also at the University of Colorado, for NASA grant NAG5-5141.) Grant NAG5-5021 provided assistance to the overall program through analysis of airglow and solar data, support of two graduate students, laboratory technical services, and field support. The general goals of the rocket program were to measure the solar extreme ultraviolet spectral irradiance, measure the terrestrial far-ultraviolet airglow, and analyze their relationship at various levels of solar activity, including near solar minimum. These have been met, as shown below. In addition, we have used the attenuation of solar radiation as the rocket descends through the thermosphere to measure density changes. This work demonstrates the maturity of the observational and modeling methods connecting energetic solar photon fluxes and airglow emissions through the processes of photoionization and photoelectron production and loss. Without a simultaneous photoelectron measurement, some aspects of this relationship remain obscure, and there are still questions pertaining to cascade contributions to molecular and atomic airglow emissions. However, by removing the solar irradiance as an "adjustable parameter" in the analysis, significant progress has been made toward understanding the relationship of far-ultraviolet airglow emissions to the solar and atmospheric conditions that control them.

Solomon, Stanley C.↗

NASA NTRS1998

Monte Carlo Calculations of Polarized Microwave Radiation Emerging from Cloud Structures

The last decade has seen tremendous growth in cloud dynamical and microphysical models that are able to simulate storms and storm systems with very high spatial resolution, typically of the order of a few kilometers. The fairly realistic distributions of cloud and hydrometeor properties that these models generate has in turn led to a renewed interest in the three-dimensional microwave radiative transfer modeling needed to understand the effect of cloud and rainfall inhomogeneities upon microwave observations. Monte Carlo methods, and particularly backwards Monte Carlo methods have shown themselves to be very desirable due to the quick convergence of the solutions. Unfortunately, backwards Monte Carlo methods are not well suited to treat polarized radiation. This study reviews the existing Monte Carlo methods and presents a new polarized Monte Carlo radiative transfer code. The code is based on a forward scheme but uses aliasing techniques to keep the computational requirements equivalent to the backwards solution. Radiative transfer computations have been performed using a microphysical-dynamical cloud model and the results are presented together with the algorithm description.

Kummerow, Christian↗