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Results for “Regional effects”

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 NTRS1984

Buckling of a sublaminate in a quasi-isotropic composite laminate

The buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite-element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results show that: (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension; (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates; and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.

Shivakumar, K. N.↗
NASA NTRS1985

Buckling of a sublaminate in a quasi-isotropic composite laminate

The buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite-element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results show that: (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension; (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates; and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.

Shivakumar, K. N.↗
NASA NTRS1990

Determination of depth-viewing volumes for stereo three-dimensional graphic displays

Real-world, 3-D, pictorial displays incorporating true depth cues via stereopsis techniques offer a potential means of displaying complex information in a natural way to prevent loss of situational awareness and provide increases in pilot/vehicle performance in advanced flight display concepts. Optimal use of stereopsis requires an understanding of the depth viewing volume available to the display designer. Suggested guidelines are presented for the depth viewing volume from an empirical determination of the effective region of stereopsis cueing (at several viewer-CRT screen distances) for a time multiplexed stereopsis display system. The results provide the display designer with information that will allow more effective placement of depth information to enable the full exploitation of stereopsis cueing. Increasing viewer-CRT screen distances provides increasing amounts of usable depth, but with decreasing fields-of-view. A stereopsis hardware system that permits an increased viewer-screen distance by incorporating larger screen sizes or collimation optics to maintain the field-of-view at required levels would provide a much larger stereo depth-viewing volume.

Parrish, Russell V.↗
NASA NTRS1972

Dynamical behavior of the polar topside ionosphere.

A review is given of magnetospheric interactions with the polar ionosphere using recent experimental and theoretical results. The effect of the polar wind is discussed with reference to the observational data of J. Hoffman. These and the results of other experiments support the concept of polar wind ion flows as a general feature of the topside ionosphere for all regions outside the plasmasphere. It is shown that most of the semi-permanent topside density features result from changes in plasma temperature and F2-region effects rather than being associated with changes in ion composition. Finally, the polar peak density enhancement is discussed in terms of recent observations of the polar cusp.

Banks, P. M.↗
NASA NTRS2003

Climate Impacts on Tropospheric Ozone and Hydroxyl

Climate change may influence tropospheric ozone and OH via several main pathways: (1) altering chemistry via temperature and humidity changes, (2) changing ozone and precursor sources via surface emissions, stratosphere-troposphere exchange, and light- ning, and (3) affecting trace gas sinks via the hydrological cycle and dry deposition. We report results from a set of coupled chemistry-climate model simulations designed to systematically study these effects. We compare the various effects with one another and with past and projected future changes in anthropogenic and natural emissions of ozone precursors. We find that white the overall impact of climate on ozone is probably small compared to emission changes, some significant seasonal and regional effects are apparent. The global effect on hydroxyl is quite large, however, similar in size to the effect of emission changes. Additionally, we show that many of the chemistry-climate links that are not yet adequately modeled are potentially important.

Shindell, Drew T.↗
NASA NTRS2004

Satellite Geopotential Anomaly Constraints for the Crust of the Greenland-Iceland Region

Satellite magnetometer observations of the Greenland-Iceland region compare quite well with lower altitude data. The satellite magnetic data suggest magnetically enhanced crust was emplaced by the Iceland Plume. Crustal thicknesses, which may be more than 30 km for the Greenland-Scotland Ridge, were obtained from inversion of the compensating terrain gravity effects that were estimated by spectral correlation analysis of the free-air gravity anomalies and terrain gravity effects. Regional magnetic anomaly maxima overlie possible thickened crust from eastern Iceland to the Greenland Coast. The Iceland-Faroe Ridge may involve thinner crust than the Greenland-Iceland portion of the Greenland-Scotland Ridge. The gravity derived crustal model exceeds a 0.7 correlation with available seismic estimates. In thermally active areas our gravity Moho estimates are systematically deeper than the seismic estimates suggesting local density reductions of the underlying lower crust/upper mantle. In south central Greenland, on the other hand, the gravity Moho estimates are shallower than seismic estimates to suggest a local enhancement of the lower crust/upper mantle density. The dichotomous crust of the Greenland-Iceland and Iceland-Faroe Ridges suggests unequal crustal development by the Iceland Plume and the Mid-Atlantic Ridge, where more crustal material may have been contributed to the North Atlantic Plate than the Eurasian Plate. A new thermal modeling scheme based on Poisson's relation between point pole gravity and thermal potentials allows estimation of magnetic crustal thicknesses. Subsequent magnetic anomaly inversion for susceptibility contrasts infers crustal development of the Greenland-Scotland Ridge by temporally variable pulses in plume strength.

vonFrese, R. R.↗
NASA NTRS1990

Depth-viewing-volume increase by collimation of stereo 3-D displays

Typical stereo 3-D displays are produced using a single-image-source, which is time-multiplexed, to present disparate, directly-viewed views (stereo pairs) of the visual scene to each eye. However, current stereoscopic viewing techniques impose severe restrictions in the effective viewing-volume of the stereo 3-D display. Recent experiments at Langley Research Center determined that the effective region of stereopsis cuing, the depth-viewing volume, increased with increasing viewer-to-screen distances. This increase was also accompanied by a decrease in the field-of-view of the system. It was postulated that collimation of the display source would dramatically increase the depth-viewing volume, as the effective accommodation distance would be near infinity, while maintaining the field-of-view at required levels. The goal of this proof-of-concept effort was to investigate whether or not a dramatic increase in depth-viewing volume for stereo 3-D displays would be provided by the application of collimated optics to the stereo display source.

Busquets, Anthony M.↗
NASA NTRS1999

Global Velocities from VLBI

Precise geodetic Very Long Baseline Interferometry (VLBI) measurements have been made since 1979 at about 130 points on all major tectonic plates, including stable interiors and deformation zones. From the data set of about 2900 observing sessions and about 2.3 million observations, useful three-dimensional velocities can be derived for about 80 sites using an incremental least-squares adjustment of terrestrial, celestial, Earth rotation and site/session-specific parameters. The long history and high precision of the data yield formal errors for horizontal velocity as low as 0.1 mm/yr, but the limitation on the interpretation of individual site velocities is the tie to the terrestrial reference frame. Our studies indicate that the effect of converting precise relative VLBI velocities to individual site velocities is an error floor of about 0.4 mm/yr. Most VLBI horizontal velocities in stable plate interiors agree with the NUVEL-1A model, but there are significant departures in Africa and the Pacific. Vertical precision is worse by a factor of 2-3, and there are significant non-zero values that can be interpreted as post-glacial rebound, regional effects, and local disturbances.

Ma, Chopo↗
NASA NTRS1997

Regional Application of an Ecosystem Production Model for Studies of Biogeochemistry in the...

The degree to which primary production, soil carbon, and trace gas fluxes in tropical forests of the Amazon are limited by moisture availability and other environmental factors was examined using an ecosystem modeling application for the country of Brazil. A regional geographic information system (GIS) serves as the data source of climate drivers, satellite images, land cover, and soil properties for input to the NASA Ames-CASA (Carnegie-Ames-Stanford Approach) model over a 8-km grid resolution. Simulation results supports the hypothesis that net primary production (NPP) is limited by cloud interception of solar radiation over the humid northwestern portion of the region. Peak annual rates for NPP of nearly 1.4 kg C m-2yr -1are localized in the seasonally dry eastern Amazon in areas that we assume are primarily deep-rooted evergreen forest cover. Regional effects of forest conversion on NPP and soil carbon content are indicated in the model results, especially in seasonally dry areas. Comparison of model flux predictions along selected eco-climatic transects reveal moisture, soil, and land use controls on gradients of ecosystem production and soil trace gas emissions (CO2, N2O, and NO). These results are used to formulate a series of research hypotheses for testing in the next phase of regional modeling, which includes recalibration of the light-use efficiency term in CASA using field measurements of NPP, and refinements of vegetation index and soil property (texture and potential rooting depth) maps for the region.

Potter, C. S.↗
NASA NTRS1989

Line-of-sight effects on spectroscopic measurements in the inner solar wind region

The effect of the integration along the line of sight on the spectral line profiles of the resonantly scattered Lyman alpha radiation emitted by low-density coronal holes at heights above 1.5 Rs from sun center is investigated. It is shown how the spectral lines from this region are influenced by the Lyman alpha emission from surrounding regions with higher densities. The coronal hole and the surrounding areas are described by a two-fluid solar wind model. It is shown that the line-of-sight effects can be important for the interpretation of the Lyman alpha spectral line measurements in the outer corona and inner solar wind.

Esser, Ruth↗
NASA NTRS1973

The nature of dark-etching rims in meteoritic taenite.

Taenite fields when etched develop a cloudy brown rim with approximate compositional limits of 25 and 40% Ni. In iron meteorites this cloudy zone is only a few microns wide, with a sharp, high-Ni edge about 1 micron from the kamacite interface and a diffuse edge several microns from the central plessite. It is always present in irons unless the meteorite has been cosmically or terrestrially reheated. X-ray and electron diffraction of grains scratched from exceptionally larger areas of cloudy taenite in the mesosiderite Estherville show that this etching zone contains a fine exsolution of kamacite. Detailed electron-probe investigations of taenite in Estherville show that there is a step in the M-shaped Ni profile at the sharp, high-Ni edge of the cloudy region, the Ni dropping suddenly from approximately 45 to 42%. It is proposed that exsolution in the cloudy region effectively froze in the Ni profile at that temperature. On subsequent cooling only the clear outer taenite continued to equilibrate with the kamacite matrix, producing the kink in the M profile. Cloudy taenite is therefore a variety of plessite differing from the usual varieties in that it forms at lower temperatures in areas much richer in Ni, and the morphology is not crystallographically oriented. Its absence can provide a sensitive indication of reheating.

Scott, E. R. D.↗
NASA NTRS1974

Polarized electromagnetic response of the moon

The strong anisotropy in Apollo 15 Lunar Surface Magnetometer (LSM) signals resulting from electromagnetic induction in the moon, forced by fluctuations of the interplanetary magnetic field, is shown to result from intense polarization of the induced field. Arguments are given to show that the anisotropy cannot be explained wholly by asymmetric lunar induction in the presence of the diamagnetic cavity, but must be related to a regional influence. The weaker Apollo 12 anisotropy may also be associated with a regional influence. The site of Apollo 15 LSM at the edge of the Imbrium Basin suggests a preliminary model for calculations based on the possibility that Imbrium and perhaps Serenitatis are sources of the regional effect. Lastly, since the very low frequency induction seems free of the anisotropy, our earlier estimate of deep conductivity remains unchanged.

Sonett, C. P.↗
NASA NTRS1976

Switchable Beamwidth Monopulse Method and System

A switchable beamwidth monopulse method and system are described. An antenna comprising a curved reflector and a first set of monopulse feeds positioned in the effective region of the airy disc of the antenna includes a second set of monopulse feeds. The second set of monopulse feeds is positioned outside the airy disc in the region of first bright airy ring. In narrow beamwidth monopulse operation, monopulse sum and difference channel patterns are obtained from the first set of feeds within the airy disc. In wide beamwidth monopulse operation, the difference channel pattern is obtained from the second set of feeds in the airy ring; the sum channel pattern is obtained by attenuation and phase shifting the sum channel signal obtained from the first set of feeds, and adding the resultant to the sum channel signal obtained from the second set of feeds. In a simplified form of the invention, the difference channel patterns for both narrow and wide beamwidth mode operation are obtained from the second set of feeds, while the sum channel patterns are obtained as described above.

Deerkoski, L. F.↗
NASA NTRS1977

Quiet Clean Short-haul Experimental Engine (QCSEE). Aerodynamic and aeromechanical performance of a 50.8 cm (20 inch) diameter 1.34 PR variable pitch fan with core flow

The fan aerodynamic and aeromechanical performance tests of the quiet clean short haul experimental engine under the wing fan and inlet with a simulated core flow are described. Overall forward mode fan performance is presented at each rotor pitch angle setting with conventional flow pressure ratio efficiency fan maps, distinguishing the performance characteristics of the fan bypass and fan core regions. Effects of off design bypass ratio, hybrid inlet geometry, and tip radial inlet distortion on fan performance are determined. The nonaxisymmetric bypass OGV and pylon configuration is assessed relative to both total pressure loss and induced circumferential flow distortion. Reverse mode performance, obtained by resetting the rotor blades through both the stall pitch and flat pitch directions, is discussed in terms of the conventional flow pressure ratio relationship and its implications upon achievable reverse thrust. Core performance in reverse mode operation is presented in terms of overall recovery levels and radial profiles existing at the simulated core inlet plane. Observations of the starting phenomena associated with the initiation of stable rotor flow during acceleration in the reverse mode are briefly discussed. Aeromechanical response characteristics of the fan blades are presented as a separate appendix, along with a description of the vehicle instrumentation and method of data reduction.

Giffin, R. G.↗
NASA NTRS1981

Closed coronal structures. III - Comparison of static models with X-ray, EUV, and radio observations

Numerical models of static coronal loops in energy balance are compared with high spatial resolution observations of extreme ultraviolet lines, broad-band X-ray emission, and interferometric observations at 2.8 cm of a solar active region. Difficulties of using scaling laws to test static models of coronal loops are reviewed. The theoretical model used for the comparison is summarized; the detailed X-ray, EUV, and microwave observations of the selected active region are presented; and the comparison of the model with the observations is performed. It is shown that simple static models with conductive flux vanishing at the loop base reproduce satisfactorily the observed properties in the upper portion of loop structures from compact, high-pressure loops in the core of the region to more extended, fainter loops and to large-scale loops interconnecting different active regions. Effects of changing loop parameters are investigated, and it is argued, that in contrast to the present approach, scaling laws cannot be used to discriminate between different static energy balance models. Some discrepancy is found between model predictions and observations for the lower sections of loop structures. Possible causes of the discrepancy are discussed.

Pallavicini, R.↗
NASA NTRS1981

Plasma lasers (a strong source of coherent radiation in astrophysics)

The generation of electromagnetic radiation from the free energy available in electron streams is discussed. The fundamental principles involved in a particular class of coherent plasma radiation sources, i.e., plasma lasers, are reviewed, focusing on three wave coupling, nonlinear parametric instabilities, and negative energy waves. The simplest case of plasma lasers, that of an unmagnetized plasma containing a finite level of density fluctuations and electrons streaming with respect to the ions, is dealt with. A much more complicated application of plasma lasers to the case of auroral kilometric radiation is then examined. The concept of free electron lasers, including the role of relativistic scattering, is elucidated. Important problems involving the escape of the excited radiation from its generation region, effects due to plasma shielding and nonlinear limits, are brought out.

Papadopoulos, K.↗
NASA NTRS1984

Solar Irradiance Variations on Active Region Time Scales

The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.

Labonte, B. J.↗