Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “biasing”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Human-display interactions: Context-specific biases

Recent developments in computer engineering have greatly enhanced the capabilities of display technology. As displays are no longer limited to simple alphanumeric output, they can present a wide variety of graphic information, using either static or dynamic presentation modes. At the same time that interface designers exploit the increased capabilities of these displays, they must be aware of the inherent limitation of these displays. Generally, these limitations can be divided into those that reflect limitations of the medium (e.g., reducing three-dimensional representations onto a two-dimensional projection) and those reflecting the perceptual and conceptual biases of the operator. The advantages and limitations of static and dynamic graphic displays are considered. Rather than enter into the discussion of whether dynamic or static displays are superior, general advantages and limitations are explored which are contextually specific to each type of display.

Kaiser, Mary Kister↗
NASA NTRS1986

An additional source of uncertainty and bias in digital spectral estimates near the Nyquist frequency

An additional source of bias and uncertainty in digital spectral estimates near the Nyquist frequency is discovered which is produced by the fact that the finite width main lobe of the spectral window is periodic with period of 2(omega sub c), equal to 4pi times the Nyquist frequency. For estimates near omega sub c, contributions from frequencies near -(omega sub c) are found to appear even for a sufficiently sampled bandlimited time history. In real-world applications, this source should be significant if the number of data points is small, and it should be of even more importance if the signal is not strictly bandlimited.

Hardin, J. C.↗
NASA NTRS1987

Plasma electron collection through biased slits in a dielectric

A large number of experimental and analytical efforts have been directed toward understanding the plasma sheath growth and discharge phenomena which lead to high-voltage solar array/space plasma interactions. An important question which has not been addressed is how the voltage gradient in the plasma sheath near the surface of such an array may affect these interactions. The purpose of the experimental study described in this paper is to examine the merging of the sheaths around biased slits in a dielectric and how this affects the collection of electrons through these slits. The data, which are obtained by emissive probes and direct measurement of the current collected through the slits, indicate that when the sheaths merge the current collection by the slits is significantly altered with the most positive slit collecting more electrons than it otherwise would. Therefore, the effect of a voltage gradient in the sheath around a solar array should be considered when evaluating solar array performance.

Carruth, M. R., Jr.↗
NASA NTRS1988

Static mechanical properties of 30 x 11.5 - 14.5, type 8 aircraft tires of bias-ply and radial-belted design

An investigation was conducted to determine the static mechanical properties of a 30 x 11.5 to 14.5, Type 8, bias-ply and radial-belted aircraft tire. The properties measured were the spring rate and damping characteristics of each tire from vertical- and lateral-loading hysteresis loops. Mass moment of inertia tests were also conducted. The results of the study are presented along with a discussion of the advantages and disadvantages of each type of tire.

Davis, Pamela A.↗
NASA NTRS1987

Static mechanical properties of 30 x 11.5-14.5, type VII, aircraft tires of bias-ply and radial-belted design

An investigation was conducted to determine the static mechanical characteristics of 30 x 115-14.5 bias-ply and radial aircraft tires. The tires were subjected to vertical and lateral loads and mass moment of inertia tests were conducted. Static load deflection curves, spring rates, hysteresis losses, and inertia data are presented along with a discussion of the advantages and disadvantages of one tire over the other.

Davis, Pamela A.↗
NASA NTRS1988

Evidence for biasing in the CfA survey

Intrinsically bright galaxies appear systematically more correlated than faint galaxies in the Center for Astrophysics redshift survey. The amplification of the two-point correlation function behaves exponentially with luminosity, being essentially flat up to the knee of the luminosity function, then increasing markedly. The amplification reaches a factor of 3.5e + or - 0.4 in the very brightest galaxies. The effect is dominated by spirals rather than ellipticals, so that the correlation function of bright spirals becomes comparable to that of normal ellipticals. Similar results are obtained whether the correlation function is measured in two or three dimensions. The effect persists to separations of a correlation length or more, and is not confined to the cores of the Virgo, Coma, and Abell 1367 clusters, suggesting that the effect is caused by biasing, that is, galaxies kindle preferentially in more clustered regions, rather than by gravitational relaxation.

Hamilton, A. J. S.↗
NASA NTRS1988

Fore-and-aft stiffness and damping characteristics of 30 x 11.5-14.5, Type VIII, bias-ply and radial-belted aircraft tires

Measurements of footprint geometrical properties and fore and aft stiffness and damping characteristics were obtained on 30 x 11.5-14.5 bias-ply and radial-belted aircraft tires. Significant differences in stiffness and damping characteristics were found between the two design types. The results show that footprint aspect ratio effects may interfere with the improved hydroplaning potential associated with the radial-belted tire operating at higher inflation pressures.

Lopez, Mercedes C.↗
NASA NTRS1989

Upwind-biased, point-implicit relaxation strategies for viscous, hypersonic flows

An upwind-biased point-implicit relaxation algorithm for obtaining the numerical solution to the governing equations for three-dimensional viscous hypersonic flows in chemical and thermal nonequilibrium is described. Details of the algorithm development, in the context of an 11-species two-temperature reacting gas model, are emphasized. Because of the point-implicit relaxation strategy, the algorithm remains stable at large Courant numbers without the necessity of solving large block-tridiagonal systems. Predictions for the hypersonic flow of air in chemical and thermal nonequilibrium (velocity = 8917 m/s, altitude = 78 km) over the Aeroassist Flight Experiment configuration, obtained on a multidomain grid, are discussed.

Gnoffo, Peter A.↗
NASA NTRS1990

Forward Bias Inhibits Single-Event Upsets

Bipolar integrated circuits more resistant to ionizing radiation. Tests show resistance of bipolar integrated logic or memory circuit by single-event upsets increased by imparting forward bias to diode constituted by buried layer of substrate and collector.

Zoutendyk, John A.↗
NASA NTRS1989

Analysis of radar images of the active volcanic zone at Krafla, Iceland: The effects of look azimuth biasing

The geomorphic expression of Mid-Ocean-Ridge (MOR) volcanism in a subaerial setting occurs uniquely on Earth in Iceland, and the most recent MOR eruptive activity has been concentrated in the Northeastern Volcanic Zone in an area known as Krafla. Within the Krafla region are many of the key morphologic elements of MOR-related basaltic volcanism, as well as volcanic explosion craters, subglacial lava shields, tectonic fissure swarms known as gjar, and basaltic-andesite flows with well developed ogives (pressure-ridges). The objective was to quantify the degree to which the basic volcanic and structural features can be mapped from directional SAR imagery as a function of the look azimuth. To accomplish this, the current expression of volcanic and tectonic constructs was independently mapped within the Krafla region on the E, W, and N-looking SAR images, as well as from SPOT Panchromatic imagery acquired in 1987. The initial observations of the E, W, and N images indicates that fresh a'a lava surfaces are extremely radar bright (rough at 3 cm to meter scales) independent of look direction; this suggests that these flows do not have strong flow direction related structures at meter and cm scales, which is consistent with typical Icelandic a'a lava surfaces in general. The basic impression from a preliminary analysis of the effects of look azimuth biasing on interpretation of the geology of an active MOR volcanic zone is that up to 30 percent of the diagnostic features can be missed at any given look direction, but that having two orthogonal look direction images is probably sufficient to prevent gross misinterpretation.

Garvin, J. B.↗
NASA NTRS1990

An upwind-biased, point-implicit relaxation algorithm for viscous, compressible perfect-gas flows

An upwind-biased, point-implicit relaxation algorithm for obtaining the numerical solution to the governing equations for three-dimensional, viscous, compressible, perfect-gas flows is described. The algorithm is derived using a finite-volume formulation in which the inviscid components of flux across cell walls are described with Roe's averaging and Harten's entropy fix with second-order corrections based on Yee's Symmetric Total Variation Diminishing scheme. Viscous terms are discretized using central differences. The relaxation strategy is well suited for computers employing either vector or parallel architectures. It is also well suited to the numerical solution of the governing equations on unstructured grids. Because of the point-implicit relaxation strategy, the algorithm remains stable at large Courant numbers without the necessity of solving large, block tri-diagonal systems. Convergence rates and grid refinement studies are conducted for Mach 5 flow through an inlet with a 10 deg compression ramp and Mach 14 flow over a 15 deg ramp. Predictions for pressure distributions, surface heating, and aerodynamics coefficients compare well with experiment data for Mach 10 flow over a blunt body.

Gnoffo, Peter A.↗
NASA NTRS1989

Annihilation of angular momentum bias during thrusting and spinning-up maneuvers

During spinning-up and thrusting maneuvers of rockets and spacecraft, undesired transverse torques (from error sources such as thruster misalignment, center-of-mass offset and thruster mismatch) perturb the angular momentum vector from its original orientation. In this paper a maneuver scheme is presented which virtually annihilates the angular momentum vector bias, even though the magnitude and direction of the perturbing body-fixed torques are unknown. In the analysis it is assumed that the torques are small and constant and that the spacecraft or rocket can be approximated by a rigid body, which may be asymmetric. Typical maneuvers of the Galileo spacecraft are simulated to demonstrate the technique.

Longuski, J. M.↗
NASA NTRS1991

Reverse bias voltage testing of 8 cm x 8cm silicon solar cells

A study is described of the reverse I-V characteristics of the largest space qualified silicon solar cells currently available (8 x 8 cm) and of reverse bias voltage (RBV) testing performed on these cells. This study includes production grade cells, both with and without cover glass. These cells span the typical output range seen in production. Initial characteristics of these cells are measured at both 28 and 60 C. These measurements show weak correlation between cell output and reverse characteristics. Analysis is presented to determine the proper conditions for RBV stress to simulate shadowing effects on a particular array design. After performing the RBV stress the characteristics of the stressed cells are remeasured. The degradation in cell performance is highly variable which exacerbates cell mismatching over time. The effect of this degradation on array lifetime is also discussed. Generalization of these results to other array configurations is also presented.

Woike, T.↗
NASA NTRS1991

Significant reduction in arc frequency biased solar cells: Observations, diagnostics, and mitigation technique(s)

A variety of experiments were performed which identify key factors contributing to the arcing of negatively biased high voltage solar cells. These efforts have led to reduction of greater than a factor of 100 in the arc frequency of a single cell following proper remediation procedures. Experiments naturally lead to and focussed on the adhesive/encapsulant that is used to bond the protective cover slip to the solar cell. An image-intensified charge coupled device (CCD) camera system recorded UV emission from arc events which occurred exclusively along the interfacial edge between the cover slip and the solar cell. Microscopic inspection of this interfacial region showed a bead of encapsulant along this entire edge. Elimination of this encapsulant bead reduced the arc frequency by two orders of magnitude. Water contamination was also identified as a key contributor which enhances arcing of the encapsulant bead along the solar cell edge. Spectrally resolved measurements of the observable UV light shows a feature assignable to OH(A-X) electronic emission, which is common for water contaminated discharges. Experiments in which the solar cell temperature was raised to 85 C showed a reduced arcing frequency, suggesting desorption of H2O. Exposing the solar cell to water vapor was shown to increase the arcing frequency. Clean dry gases such as O2, N2, and Ar show no enhancement of the arcing rate. Elimination of the exposed encapsulant eliminates any measurable sensitivity to H2O vapor.

Upschulte, B. L.↗
NASA NTRS1990

Threshold voltage for arcing on negatively biased solar arrays

The arcing that has been found to occur when negatively biased high-voltage solar arrays in LEO lie at a critical voltage with respect to the plasma environment is presently proposed to be due to a breakdown of gas emitted under electron bombardment from the solar cells' cover-glass. The elements of the model for this phenomenon include an electron current flow from the interconnect to a neighboring cover-glass, which desorbs neutral molecules under the electron bombardment. The neutral molecules form a gas over the interconnect, and this gas breaks down when the voltage over the interconnect is sufficiently high. Specific scaling predictions are made on the basis of the geometric structure and gas in question.

Hastings, Daniel E.↗
NASA NTRS1991

The effect of the degree of wave development on the sea state bias in radar altimetry measurement

The extent by which the wave development affects the sea state bias (SSB) in the Geosat altimeter height measurements is investigated. It is shown that the altimetric SSB is not a linear function of the wave height but that it also depends on other factors of wave development, particularly on the wave age (defined as the ratio of the phase speed of the dominant ocean waves to the ocean wind speed). The wave age can be estimated crudely, as the so-called 'pseudo-wave age', on the basis of the significant wave height H(1/3) and the wind speed measured by the altimeter. The analysis of 2.7 years' worth of Geosat data showed a general trend for the dependence of the SSB on the pseudo-wave age, which agrees well with the theoretical prediction that, for a given H(1/3), the SSB decreases as the pseudo-wave age increases.

Fu, Lee-Lueng↗
NASA NTRS1990

Forward-biased current annealing of radiation degraded indium phosphide and gallium arsenide solar cells

The preliminary results of a novel approach to low-temperature annealing of previously irradiated indium phosphide and gallium arsenide solar cells are reported. The technique is based on forward-biased current annealing. The two types of III-V solar cells were irradiated with 1-MeV electrons to a fluence level of (1-10) x 10 to the 14th electrons/sq cm. Several annealing attempts were made, varying all conditions. Optimum annealing was achieved when cells were injected with minority currents at a constant 90 C. The current density for each type of cell was also determined. Significant recovery of degraded parameters was achieved in both cases. However, the InP cell recovery notably exceeded the recovery in GaAs cells. The recovery is thought to be caused by current-stimulated reordering of the radiator-induced displacement damage. Both types of cell were then subjected to several cycles of irradiation and annealing. The results were also very promising. The significant recovery of degraded cell parameters at low temperature might play a major role in considerably extending the end of life of future spacecraft.

Michael, Sherif↗
NASA NTRS1992

Eliminating Bias In Acousto-Optical Spectrum Analysis

Scheme for digital processing of video signals in acousto-optical spectrum analyzer provides real-time correction for signal-dependent spectral bias. Spectrum analyzer described in "Two-Dimensional Acousto-Optical Spectrum Analyzer" (NPO-18092), related apparatus described in "Three-Dimensional Acousto-Optical Spectrum Analyzer" (NPO-18122). Essence of correction is to average over digitized outputs of pixels in each CCD row and to subtract this from the digitized output of each pixel in row. Signal processed electro-optically with reference-function signals to form two-dimensional spectral image in CCD camera.

Ansari, Homayoon↗