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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Reliable samples of quasars and hot stars from a spectrophotometric survey of the U.S. catalogs

The U.S. survey for blue- and ultraviolet-excess starlike objects is reviewed, focusing on the features which have contributed to its accuracy. The spectrophotometric survey is described in terms of the observational setup and procedures. It is suggested that the survey has produced reliably classified samples of quasars and hot evolved stars and that the procedures used in the study provide a means of deriving distance and luminosity information about these objects. Several cumulative number counts and spectra of a DA white dwarf and a quasar with prominent C IV and C III emission are given as examples.

Mitchell, Kenneth J.↗
NASA NTRS1995

Semianalytic continuum spectra of Type 2 supernovae

We extend the approximate radiative transfer analysis of Hershkowitz, Linder, & Wagoner (1986) to a more general class of supernova model atmospheres, using a simple fit to the effective continuum opacity produced by lines (Wagoner, Perez, & Vasu 1991). At the low densities considered, the populations of the excited states of hydrogen are governed mainly by photoionization and recombination, and scattering dominates absorptive opacity. We match the asymptotic expressions for the spectral energy density J(sub nu) at the photosphere, whose location at each frequency is determined by a first-order calculation of the deviation of J(sub nu) from the Planck function B(sub nu). The emergent spectral luminosity then assumes the form L(sub nu) = 4 pi(squared)r(squared)(sub *) zeta(squared)B(sub nu)(T(sub p)), where T(sub p)(nu) is the photospheric temperature zeta is the dilution factor, and r(sub *) is a fiducial radius (ultimately taken to be the photospheric radius r(sub p)(nu)). The atmosphere is characterized by an effective temperature T(sub e) (varies as L(sup 1/4)r(sup -1/2)(sub *)) and hydrogen density n(sub H) = dependence of zeta on frequency nu and the parameters T(sub p), r(sub p), and alpha. The resulting understanding of the dependence of the spectral luminosity on observable parameters which characterize the relevant physical conditions will be of particular use in assessing the reliability of the expanding photosphere method of distance determination. This is particularly important at cosmological distances, where no information about the progenitor star will be available. This technique can also be applied to other low-density photosphere.

Montes, Marcos J.↗
NASA NTRS2002

Study of Lightweight Ni-Co Alloy Mirrors Obtained by Electroforming Techniques

One contribution in reducing the costs of optics in space can be provided by production of ultralight mirrors. The decrease in the weight of the primary mirror of a telescope is anticipated to lead to the possibility of increasing the size of the telescopes, therefore increasing the amount and distance from which information is received. An electroplating process of ultralight replica mirrors from nickel sulfamate solution will be described. Based on an experimental setup with cylindrical symmetry, flat mirrors with a diameter of 7 inches and thickness of 1.5 mm are made from a Ni-Co alloy. The composition of the resulting deposit is analyzed using Rutherford Backscattering Spectrometry (RBS) and Proton Induced X-ray Emission (PIXE). In order to resolve Ni and Co, 10 MeV nitrogen ions are used as projectiles in the RBS measurements. Solution parameters monitored during the deposition process using optical absorption and polarography will be correlated with the final concentration of Ni and Co in the deposit. Bath parameters like temperature, current density, agitation level and acidity are chosen at certain values and maintained constant from one sample to another throughout the deposition process. The purpose of the experiment is to obtain mirrors with near zero stress, and predetermined composition and hardness. This study is an intermediate step in obtaining through the same process, but with a larger scale setup, ultralight large aperture replica mirrors.

Jones, Ruth↗
NASA NTRS2006

Pilot Navigation Errors on the Airport Surface: Identifying Contributing Factors and Mitigating Solutions

A taxonomy of navigation errors (pilot deviations) during taxi operations was developed that defines 3 classes of errors: planning, decision, and execution errors. This taxonomy was applied to error data from 2 full-mission simulation studies that included trials that replicated current-day operations and trials with advanced cockpit technologies including datalink, electronic moving maps (EMM), and head-up displays (HUDs). Pilots committed navigation errors on 17% of current-day operations trials (in low-visibility and night), distributed roughly equally across the 3 error classes. Each error class was associated with a unique set of contributing factor s and mitigating solutions. Planning errors were mitigated by technologies that provided an unambiguous record of the clearance (datalink and the EMM, which possessed a text-based clearance). Decision errors were mitigated by technologies that provided both local and global awareness including information about the distance to and direction of the next turn, current township location, and a graphical depiction of the route (as provided by the EMM and HUD together). Execution errors were best mitigated by the HUD, which disambiguated the environment and depicted the clear ed taxi route. Implications for technology design and integration are provided.

Hooey, Becky L.↗
NASA NTRS2009

Measurement of Trap Length for an Optical Trap

The trap length along the beam axis for an optical trap formed with an upright, oil-immersion microscope was measured. The goals for this effort were twofold. It was deemed useful to understand the depth to which an optical trap can reach for purposes of developing a tool to assist in the fabrication of miniature devices. Additionally, it was desired to know whether the measured trap length favored one or the other of two competing theories to model an optical trap. The approach was to trap a microsphere of known size and mass and raise it from its initial trap position. The microsphere was then dropped by blocking the laser beam for a pre-determined amount of time. Dropping the microsphere in a free-fall mode from various heights relative to the coverslip provides an estimate of how the trapping length changes with depth in water in a sample chamber on a microscope slide. While it was not possible to measure the trap length with sufficient precision to support any particular theory of optical trap formation, it was possible to find regions where the presence of physical boundaries influenced optical traps, and determine that the trap length, for the apparatus studied, is between 6 and 7 m. These results allow more precise control using optical micromanipulation to assemble miniature devices by providing information about the distance over which an optical trap is effective.

Wrbanek, Susan Y.↗
NASA NTRS2018

Sun-to-Earth Propagation of the 2015 June 21 Coronal Mass Ejection Revealed by Optical, EUV, and Radio Observations

We investigate the propagation of the 2015 June 21 CME-driven shock as revealed by the type II bursts at metricand longer wavelengths and coronagraph observations. The CME was associated with the second largest geomagneticstorm of solar cycle 24 and a large solar energetic particle (SEP) event. The eruption consisted of twoM-class flares, with the first one being confined, with no metric or interplanetary radio bursts. However, therewas intense microwave burst, indicating accelerated particles injected toward the Sun. The second flare was eruptive that resulted in a halo CME. The CME was deflected primarily by an equatorial coronal hole that resulted in the modification of the intensity profile of the associated SEP event and the duration of the CME at Earth. The interplanetary type II burst was particularly intense and was visible from the corona all the way to the vicinity of the Wind spacecraft with fundamental-harmonic structure. We computed the shock speed using the type II drift rates at various heliocentric distances and obtained information on the evolution of the shock that matched coronagraph observations near the Sun and in-situ observations near Earth. The depth of the geomagnetic storm is consistent with the 1-AU speed of the CME and the magnitude of the southward component.

Gopalswamy, N.↗
NASA NTRS1979

Algorithms and logic for incorporating ILS NASA TCV B-737 airplane area navigation system

The algorithms and logic for use in the implementation of instrument landing system (ILS) localizer deviation signals for the generation of navigation and guidance information are presented. The navigation position estimates, based on range information from a randomly chosen distance measuring equipment (DME) and ILS localizer deviation information, are illustrated. The ILS volumetric coverage and DME geometric checks are described and their addition to area navigation systems with minimum software modification are discussed.

Knox, C. E.↗
NASA NTRS1984

The distribution of interstellar matter toward Tycho's supernova remnant and its relation to distance estimates

Observations of interstellar absorption lines in the spectra of five stars in the direction of Tycho's Supernova Remnant are presented. The profiles show significant absorption at large negative velocities, - 50 to - 60 km/s (LSR). This information, together with the distances of the background stars, permits limiting distances to be assigned to the corresponding velocity components in the H I 21-cm line absorption spectrum of the supernova remnant itself. The 21-cm absorption line data for Tycho's Supernova Remnant are entirely consistent with a distance as small as 2 kpc. Distances based upon simple kinematic models of galactic rotation can be confused by well-known noncircular motions in this direction. The interstellar line data also reveal a relatively high column density of CO toward HD 108.

Black, J. H.↗
NASA NTRS2020

Local Food Crop Production can Fulfil Demand for Less than One-Third of the Population

The distance between the origin and end-point of food supply chains, and the ‘localness’ of food systems, are key considerations of many narratives associated with sustainability. Yet, information on the minimum distance to food crops is still scarce at the global level. Using an optimization model based on ‘foodsheds’ (that is, self-sufficient areas with internal dependencies), we calculate the potential minimum distance between food production and consumption for six crop types around the world. We show that only 11–28% of the global population can fulfil their demand for specific crops within a 100-km radius, with substantial variation between different regions and crops. For 26–64% of the population, that distance is greater than 1,000 km. Even if transnational foodsheds were in place, large parts of the globe would still depend on trade to feed themselves. Although yield gap closure and food loss reductions could favour more local food systems, particularly in Africa and Asia, global supply chains would still be needed to ensure an adequate and stable food supply.

Crop production↗
NASA NTRS1970

Image resolution: Its significance in a wildland area

The information content of simulated space photos as a function of various levels of image resolution was determined by identifying major vegetation-terrain types in a series of images purposely degraded optically to different levels of ground resolution resolvable distance. Comparison of cumulative interpretation results with actual ground truth data indicates that although there is definite decrease in interpretability as ground resolvable distance increases, some valuable information is gained by using even the poorest aerial photography. Developed is the importance of shape and texture for correct identification of broadleaf or coniferous vegetation types and the relative unimportance of shape and texture for the recognition of grassland, water bodies, and nonvegetated areas. Imagery must have a ground resolvable distance of at least 50 feet to correctly discriminate between primary types of woody vegetation.

Lauer, D. T.↗
NASA NTRS1990

A computational model for dynamic vision

This paper describes a novel computational model for dynamic vision which promises to be both powerful and robust. Furthermore the paradigm is ideal for an active vision system where camera vergence changes dynamically. Its basis is the retinotopically indexed object-centered encoding of the early visual information. Specifically, the relative distances of objects to a set of referents is encoded in image registered maps. To illustrate the efficacy of the method, it is applied to the problem of dynamic stereo vision. Integration of depth information over multiple frames obtained by a moving robot generally requires precise information about the relative camera position from frame to frame. Usually, this information can only be approximated. The method facilitates the integration of depth information without direct use or knowledge of camera motion.

Moezzi, Saied↗
NASA NTRS2007

Learning and Prediction of Slip from Visual Information

This paper presents an approach for slip prediction from a distance for wheeled ground robots using visual information as input. Large amounts of slippage which can occur on certain surfaces, such as sandy slopes, will negatively affect rover mobility. Therefore, obtaining information about slip before entering such terrain can be very useful for better planning and avoiding these areas. To address this problem, terrain appearance and geometry information about map cells are correlated to the slip measured by the rover while traversing each cell. This relationship is learned from previous experience, so slip can be predicted remotely from visual information only. The proposed method consists of terrain type recognition and nonlinear regression modeling. The method has been implemented and tested offline on several off-road terrains including: soil, sand, gravel, and woodchips. The final slip prediction error is about 20%. The system is intended for improved navigation on steep slopes and rough terrain for Mars rovers.

rover↗
NASA NTRS2004

Modeling Forest Understory Fires in an Eastern Amazonian Landscape

Forest understory fires are an increasingly important cause of forest impoverishment in Ammonia, but little is known of the landscape characteristics and climatic phenomena that determine their occurrence. We developed empirical functions relating the occurrence of understory fires to landscape features near Paragominas, a 35- yr-old ranching and logging center in eastern Ammonia. An historical sequence of maps of forest understory fire was created based on field interviews With local farmers and Landsat TM images. Several landscape features that might explain spatial variations in the occurrence of understory fires were also mapped and co-registered for each of the sample dates, including: forest fragment size and shape, forest impoverishment through logging and understory fires, source of ignition (settlements and charcoal pits), roads, forest edges, and others. The spatial relationship between forest understory fire and each landscape characteristic was tested by regression analyses. Fire probability models were then developed for various combinations of landscape characteristics. The analyses were conducted separately for years of the El Nino Southern Oscillation (ENSO), which are associated with severe drought in eastern Amazonia, and non-ENS0 years. Most (91 %) of the forest area that burned during the 10-yr sequence caught fire during ENSO years, when severe drought may have increased both forest flammability and the escape of agricultural management fires. Forest understory fires were associated with forest edges, as reported in previous studies from Ammonia. But the strongest predictor of forest fire was the percentage of the forest fragment that had been previously logged or burned. Forest fragment size, distance to charcoal pits, distance to agricultural settlement, proximity to forest edge, and distance to roads were also correlated with forest understory fire. Logistic regression models using information on fragment degradation and distance to ignition sources accurately predicted the location of lss than 80% of the forest fires observed during the ENSO event of 1997- 1998. In this Amazon landscape, forest understory fire is a complex function of several variables that influence both the flammability and ignition exposure of the forest.

Alencar, A. A. C.↗
NASA NTRS1986

Early photometry of comet p/Halley - Development of the coma

The observation of comets over a large range of heliocentric distances can provide important information, taking into account, for instance, the appearance of true cometary characteristics. Photometric evidence is provided regarding coma formation at approximately 5.9 AU, giving attention to aspects of water-ice sublimation. New photometry of p/Halley was obtained when the comet was at 5.9 and 5.1 AU, during 1984 October and 1985 January, respectively. The new observations are compared with data obtained at larger heliocentric distances. It is argued that sustained mass loss from the nucleus began at about 5.9 AU, at a rate which is consistent with production by sublimation from a predominantly water-ice nucleus.

Meech, K. J.↗
NASA NTRS1972

Inversion of radiation data in biophysics

Topics in biophysics are summarized in which radiation data inversion problems occur. The topics fall into two main categories. The first relates to information acquired about the distance environment through seeing, hearing, etc. The second relates to the use of electromagnetic, acoustic, or other radiation for diagnostic purposes, either at a bulk or a molecular level.

Twersky, V.↗
NASA NTRS1985

Cluster redshifts in five suspected superclusters

Redshift surveys for rich superclusters were carried out in five regions of the sky containing surface-density enhancements of Abell clusters. While several superclusters are identified, projection effects dominate each field, and no system contains more than five rich clusters. Two systems are found to be especially interesting. The first, field 0136 10, is shown to contain a superposition of at least four distinct superclusters, with the richest system possessing a small velocity dispersion. The second system, 2206 - 22, though a region of exceedingly high Abell cluster surface density, appears to be a remarkable superposition of 23 rich clusters almost uniformly distributed in redshift space between 0.08 and 0.24. The new redshifts significantly increase the three-dimensional information available for the distance class 5 and 6 Abell clusters and allow the spatial correlation function around rich superclusters to be estimated.

Ciardullo, R.↗
NASA NTRS1995

Advanced Payload Transfer Measurement System (APT-MS) Mechanical Features

During the last two feet or so of transfer, for a large or heavy payload to its restraining fixture, the consequences of unplanned contact (or impact) between payload and support structure can range from merely annoying to something approaching disaster. Current transfer methods employ technicians with meter sticks stationed at the various hold-down locations to estimate the distances to contact. This information is communicated orally to the crane operator. It is understandable that this work proceeds carefully and therefore slowly. The objectives of this study are (1) to explore mechanical sources of measurement error; and (2) to develop an improved prototype design that is compact, inexpensive, and addresses the measurement error issues. APT is a relatively inexpensive electro-mechanical device that reduces both time and manpower required to make shuttle payload transfers. APT measurement system would provide a GUI for the 'move-conductor' (crane operator) so he could see the displacements of all hold-down interfaces as they move together and thus have a more accurate, comprehensive and 'real-time' picture of the engagement activity. An error model attempts to include all estimatable sources of mechanical error and design features were introduced to reduce or eliminate major sources of error.

Brewer, William V.↗